diff --git a/packages/react-reconciler/src/ReactFiberBeginWork.js b/packages/react-reconciler/src/ReactFiberBeginWork.js
index 2231dc5ae5b6..014782b2fd6d 100644
--- a/packages/react-reconciler/src/ReactFiberBeginWork.js
+++ b/packages/react-reconciler/src/ReactFiberBeginWork.js
@@ -179,6 +179,7 @@ import {
   scheduleUpdateOnFiber,
   renderDidSuspendDelayIfPossible,
   markUnprocessedUpdateTime,
+  getWorkInProgressRoot,
 } from './ReactFiberWorkLoop';
 
 const ReactCurrentOwner = ReactSharedInternals.ReactCurrentOwner;
@@ -1590,6 +1591,35 @@ function shouldRemainOnFallback(
   );
 }
 
+function getRemainingWorkInPrimaryTree(
+  workInProgress,
+  currentChildExpirationTime,
+  renderExpirationTime,
+) {
+  if (currentChildExpirationTime < renderExpirationTime) {
+    // The highest priority remaining work is not part of this render. So the
+    // remaining work has not changed.
+    return currentChildExpirationTime;
+  }
+  if ((workInProgress.mode & BlockingMode) !== NoMode) {
+    // The highest priority remaining work is part of this render. Since we only
+    // keep track of the highest level, we don't know if there's a lower
+    // priority level scheduled. As a compromise, we'll render at the lowest
+    // known level in the entire tree, since that will include everything.
+    // TODO: If expirationTime were a bitmask where each bit represents a
+    // separate task thread, this would be: currentChildBits & ~renderBits
+    const root = getWorkInProgressRoot();
+    if (root !== null) {
+      const lastPendingTime = root.lastPendingTime;
+      if (lastPendingTime < renderExpirationTime) {
+        return lastPendingTime;
+      }
+    }
+  }
+  // In legacy mode, there's no work left.
+  return NoWork;
+}
+
 function updateSuspenseComponent(
   current,
   workInProgress,
@@ -1831,8 +1861,15 @@ function updateSuspenseComponent(
             fallbackChildFragment.return = workInProgress;
             primaryChildFragment.sibling = fallbackChildFragment;
             fallbackChildFragment.effectTag |= Placement;
-            primaryChildFragment.childExpirationTime = NoWork;
-
+            primaryChildFragment.childExpirationTime = getRemainingWorkInPrimaryTree(
+              workInProgress,
+              // This argument represents the remaining work in the current
+              // primary tree. Since the current tree did not already time out
+              // the direct parent of the primary children is the Suspense
+              // fiber, not a fragment.
+              current.childExpirationTime,
+              renderExpirationTime,
+            );
             workInProgress.memoizedState = SUSPENDED_MARKER;
             workInProgress.child = primaryChildFragment;
 
@@ -1895,6 +1932,11 @@ function updateSuspenseComponent(
         );
         fallbackChildFragment.return = workInProgress;
         primaryChildFragment.sibling = fallbackChildFragment;
+        primaryChildFragment.childExpirationTime = getRemainingWorkInPrimaryTree(
+          workInProgress,
+          currentPrimaryChildFragment.childExpirationTime,
+          renderExpirationTime,
+        );
         primaryChildFragment.childExpirationTime = NoWork;
         // Skip the primary children, and continue working on the
         // fallback children.
@@ -1989,7 +2031,15 @@ function updateSuspenseComponent(
         fallbackChildFragment.return = workInProgress;
         primaryChildFragment.sibling = fallbackChildFragment;
         fallbackChildFragment.effectTag |= Placement;
-        primaryChildFragment.childExpirationTime = NoWork;
+        primaryChildFragment.childExpirationTime = getRemainingWorkInPrimaryTree(
+          workInProgress,
+          // This argument represents the remaining work in the current
+          // primary tree. Since the current tree did not already time out
+          // the direct parent of the primary children is the Suspense
+          // fiber, not a fragment.
+          current.childExpirationTime,
+          renderExpirationTime,
+        );
         // Skip the primary children, and continue working on the
         // fallback children.
         workInProgress.memoizedState = SUSPENDED_MARKER;
@@ -3006,6 +3056,42 @@ function beginWork(
                 renderExpirationTime,
               );
             } else {
+              // The primary child fragment does not have pending work marked
+              // on it...
+
+              // ...usually. There's an unfortunate edge case where the fragment
+              // fiber is not part of the return path of the children, so when
+              // an update happens, the fragment doesn't get marked during
+              // setState. This is something we should consider addressing when
+              // we refactor the Fiber data structure. (There's a test with more
+              // details; to find it, comment out the following block and see
+              // which one fails.)
+              //
+              // As a workaround, we need to recompute the `childExpirationTime`
+              // by bubbling it up from the next level of children. This is
+              // based on similar logic in `resetChildExpirationTime`.
+              let primaryChild = primaryChildFragment.child;
+              while (primaryChild !== null) {
+                const childUpdateExpirationTime = primaryChild.expirationTime;
+                const childChildExpirationTime =
+                  primaryChild.childExpirationTime;
+                if (
+                  (childUpdateExpirationTime !== NoWork &&
+                    childUpdateExpirationTime >= renderExpirationTime) ||
+                  (childChildExpirationTime !== NoWork &&
+                    childChildExpirationTime >= renderExpirationTime)
+                ) {
+                  // Found a child with an update with sufficient priority.
+                  // Use the normal path to render the primary children again.
+                  return updateSuspenseComponent(
+                    current,
+                    workInProgress,
+                    renderExpirationTime,
+                  );
+                }
+                primaryChild = primaryChild.sibling;
+              }
+
               pushSuspenseContext(
                 workInProgress,
                 setDefaultShallowSuspenseContext(suspenseStackCursor.current),
diff --git a/packages/react-reconciler/src/ReactFiberRoot.js b/packages/react-reconciler/src/ReactFiberRoot.js
index d035d31c764f..544dcd076414 100644
--- a/packages/react-reconciler/src/ReactFiberRoot.js
+++ b/packages/react-reconciler/src/ReactFiberRoot.js
@@ -65,6 +65,8 @@ type BaseFiberRootProperties = {|
   callbackPriority: ReactPriorityLevel,
   // The earliest pending expiration time that exists in the tree
   firstPendingTime: ExpirationTime,
+  // The latest pending expiration time that exists in the tree
+  lastPendingTime: ExpirationTime,
   // The earliest suspended expiration time that exists in the tree
   firstSuspendedTime: ExpirationTime,
   // The latest suspended expiration time that exists in the tree
@@ -122,6 +124,7 @@ function FiberRootNode(containerInfo, tag, hydrate) {
   this.callbackNode = null;
   this.callbackPriority = NoPriority;
   this.firstPendingTime = NoWork;
+  this.lastPendingTime = NoWork;
   this.firstSuspendedTime = NoWork;
   this.lastSuspendedTime = NoWork;
   this.nextKnownPendingLevel = NoWork;
@@ -205,6 +208,10 @@ export function markRootUpdatedAtTime(
   if (expirationTime > firstPendingTime) {
     root.firstPendingTime = expirationTime;
   }
+  const lastPendingTime = root.lastPendingTime;
+  if (lastPendingTime === NoWork || expirationTime < lastPendingTime) {
+    root.lastPendingTime = expirationTime;
+  }
 
   // Update the range of suspended times. Treat everything lower priority or
   // equal to this update as unsuspended.
@@ -232,6 +239,11 @@ export function markRootFinishedAtTime(
 ): void {
   // Update the range of pending times
   root.firstPendingTime = remainingExpirationTime;
+  if (remainingExpirationTime < root.lastPendingTime) {
+    // This usually means we've finished all the work, but it can also happen
+    // when something gets downprioritized during render, like a hidden tree.
+    root.lastPendingTime = remainingExpirationTime;
+  }
 
   // Update the range of suspended times. Treat everything higher priority or
   // equal to this update as unsuspended.
diff --git a/packages/react-reconciler/src/__tests__/ReactSuspenseList-test.internal.js b/packages/react-reconciler/src/__tests__/ReactSuspenseList-test.internal.js
index 12a6d03a2313..7928ca491b08 100644
--- a/packages/react-reconciler/src/__tests__/ReactSuspenseList-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/ReactSuspenseList-test.internal.js
@@ -293,7 +293,13 @@ describe('ReactSuspenseList', () => {
 
     await C.resolve();
 
-    expect(Scheduler).toFlushAndYield(['C']);
+    expect(Scheduler).toFlushAndYield([
+      // TODO: Ideally we wouldn't have to retry B. This is an implementation
+      // trade off.
+      'Suspend! [B]',
+
+      'C',
+    ]);
 
     expect(ReactNoop).toMatchRenderedOutput(
       <>
diff --git a/packages/react-reconciler/src/__tests__/ReactSuspenseWithNoopRenderer-test.internal.js b/packages/react-reconciler/src/__tests__/ReactSuspenseWithNoopRenderer-test.internal.js
index 7107a87c3efe..55793fb6c3b3 100644
--- a/packages/react-reconciler/src/__tests__/ReactSuspenseWithNoopRenderer-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/ReactSuspenseWithNoopRenderer-test.internal.js
@@ -3,11 +3,12 @@ let ReactFeatureFlags;
 let Fragment;
 let ReactNoop;
 let Scheduler;
-let ReactCache;
 let Suspense;
+let textCache;
 
-let TextResource;
-let textResourceShouldFail;
+let readText;
+let resolveText;
+let rejectText;
 
 describe('ReactSuspenseWithNoopRenderer', () => {
   if (!__EXPERIMENTAL__) {
@@ -26,26 +27,74 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     Fragment = React.Fragment;
     ReactNoop = require('react-noop-renderer');
     Scheduler = require('scheduler');
-    ReactCache = require('react-cache');
     Suspense = React.Suspense;
 
-    TextResource = ReactCache.unstable_createResource(
-      ([text, ms = 0]) => {
-        return new Promise((resolve, reject) =>
-          setTimeout(() => {
-            if (textResourceShouldFail) {
-              Scheduler.unstable_yieldValue(`Promise rejected [${text}]`);
-              reject(new Error('Failed to load: ' + text));
-            } else {
-              Scheduler.unstable_yieldValue(`Promise resolved [${text}]`);
-              resolve(text);
-            }
-          }, ms),
-        );
-      },
-      ([text, ms]) => text,
-    );
-    textResourceShouldFail = false;
+    textCache = new Map();
+
+    readText = text => {
+      const record = textCache.get(text);
+      if (record !== undefined) {
+        switch (record.status) {
+          case 'pending':
+            throw record.promise;
+          case 'rejected':
+            throw Error('Failed to load: ' + text);
+          case 'resolved':
+            return text;
+        }
+      } else {
+        let ping;
+        const promise = new Promise(resolve => (ping = resolve));
+        const newRecord = {
+          status: 'pending',
+          ping: ping,
+          promise,
+        };
+        textCache.set(text, newRecord);
+        throw promise;
+      }
+    };
+
+    resolveText = text => {
+      const record = textCache.get(text);
+      if (record !== undefined) {
+        if (record.status === 'pending') {
+          Scheduler.unstable_yieldValue(`Promise resolved [${text}]`);
+          record.ping();
+          record.ping = null;
+          record.status = 'resolved';
+          clearTimeout(record.promise._timer);
+          record.promise = null;
+        }
+      } else {
+        const newRecord = {
+          ping: null,
+          status: 'resolved',
+          promise: null,
+        };
+        textCache.set(text, newRecord);
+      }
+    };
+
+    rejectText = text => {
+      const record = textCache.get(text);
+      if (record !== undefined) {
+        if (record.status === 'pending') {
+          Scheduler.unstable_yieldValue(`Promise rejected [${text}]`);
+          record.ping();
+          record.status = 'rejected';
+          clearTimeout(record.promise._timer);
+          record.promise = null;
+        }
+      } else {
+        const newRecord = {
+          ping: null,
+          status: 'rejected',
+          promise: null,
+        };
+        textCache.set(text, newRecord);
+      }
+    };
   });
 
   // function div(...children) {
@@ -83,12 +132,17 @@ describe('ReactSuspenseWithNoopRenderer', () => {
   function AsyncText(props) {
     const text = props.text;
     try {
-      TextResource.read([props.text, props.ms]);
+      readText(text);
       Scheduler.unstable_yieldValue(text);
       return <span prop={text} />;
     } catch (promise) {
       if (typeof promise.then === 'function') {
         Scheduler.unstable_yieldValue(`Suspend! [${text}]`);
+        if (typeof props.ms === 'number' && promise._timer === undefined) {
+          promise._timer = setTimeout(() => {
+            resolveText(text);
+          }, props.ms);
+        }
       } else {
         Scheduler.unstable_yieldValue(`Error! [${text}]`);
       }
@@ -279,7 +333,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     expect(ReactNoop.getChildren()).toEqual([]);
 
     // Wait for data to resolve
-    await advanceTimers(100);
+    await resolveText('B');
     // Renders successfully
     expect(Scheduler).toHaveYielded(['Promise resolved [B]']);
     expect(Scheduler).toFlushAndYield(['A', 'B', 'C', 'D']);
@@ -329,10 +383,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     expect(Scheduler).toFlushAndYield(['Suspend! [Result]', 'Loading...']);
     expect(ReactNoop.getChildren()).toEqual([]);
 
-    textResourceShouldFail = true;
-    ReactNoop.expire(1000);
-    await advanceTimers(1000);
-    textResourceShouldFail = false;
+    await rejectText('Result');
 
     expect(Scheduler).toHaveYielded(['Promise rejected [Result]']);
 
@@ -382,10 +433,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     expect(Scheduler).toFlushAndYield(['Suspend! [Result]', 'Loading...']);
     expect(ReactNoop.getChildren()).toEqual([span('Loading...')]);
 
-    textResourceShouldFail = true;
-    ReactNoop.expire(3000);
-    await advanceTimers(3000);
-    textResourceShouldFail = false;
+    await rejectText('Result');
 
     expect(Scheduler).toHaveYielded(['Promise rejected [Result]']);
     expect(Scheduler).toFlushAndYield([
@@ -416,7 +464,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     // Initial mount
     ReactNoop.render(<App highPri="A" lowPri="1" />);
     expect(Scheduler).toFlushAndYield(['A', 'Suspend! [1]', 'Loading...']);
-    await advanceTimers(0);
+    await resolveText('1');
     expect(Scheduler).toHaveYielded(['Promise resolved [1]']);
     expect(Scheduler).toFlushAndYield(['A', '1']);
     expect(ReactNoop.getChildren()).toEqual([span('A'), span('1')]);
@@ -439,7 +487,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     expect(ReactNoop.getChildren()).toEqual([span('B'), span('1')]);
 
     // Unblock the low-pri text and finish
-    await advanceTimers(0);
+    await resolveText('2');
     expect(Scheduler).toHaveYielded(['Promise resolved [2]']);
     expect(ReactNoop.getChildren()).toEqual([span('B'), span('1')]);
   });
@@ -472,7 +520,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     expect(Scheduler).toFlushAndYield(['Suspend! [A]', 'B', 'Loading...']);
     expect(ReactNoop.getChildren()).toEqual([]);
 
-    await advanceTimers(0);
+    await resolveText('A');
     expect(Scheduler).toHaveYielded(['Promise resolved [A]']);
     expect(Scheduler).toFlushAndYield(['A', 'B']);
     expect(ReactNoop.getChildren()).toEqual([span('A'), span('B')]);
@@ -711,7 +759,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     expect(ReactNoop.getChildren()).toEqual([span('Loading...'), span('Sync')]);
 
     // Once the promise resolves, we render the suspended view
-    await advanceTimers(0);
+    await resolveText('Async');
     expect(Scheduler).toHaveYielded(['Promise resolved [Async]']);
     expect(Scheduler).toFlushAndYield(['Async']);
     expect(ReactNoop.getChildren()).toEqual([span('Async'), span('Sync')]);
@@ -1212,7 +1260,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
           const text = props.text;
           Scheduler.unstable_yieldValue('constructor');
           try {
-            TextResource.read([props.text, props.ms]);
+            readText(text);
             this.state = {text};
           } catch (promise) {
             if (typeof promise.then === 'function') {
@@ -1245,7 +1293,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
       ]);
       expect(ReactNoop.getChildren()).toEqual([span('Loading...')]);
 
-      await advanceTimers(1000);
+      await resolveText('Hi');
 
       expect(Scheduler).toHaveYielded(['Promise resolved [Hi]']);
       expect(Scheduler).toFlushExpired([
@@ -1287,6 +1335,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
         'Suspend! [Hi]',
         'Loading...',
         // Re-render due to lifecycle update
+        'Suspend! [Hi]',
         'Loading...',
       ]);
       expect(ReactNoop.getChildren()).toEqual([span('Loading...')]);
@@ -1495,9 +1544,8 @@ describe('ReactSuspenseWithNoopRenderer', () => {
       }
       render() {
         const text = this.props.text;
-        const ms = this.props.ms;
         try {
-          TextResource.read([text, ms]);
+          readText(text);
           Scheduler.unstable_yieldValue(text);
           return <span prop={text} />;
         } catch (promise) {
@@ -1581,9 +1629,8 @@ describe('ReactSuspenseWithNoopRenderer', () => {
         };
       }, [props.text]);
       const text = props.text;
-      const ms = props.ms;
       try {
-        TextResource.read([text, ms]);
+        readText(text);
         Scheduler.unstable_yieldValue(text);
         return <span prop={text} />;
       } catch (promise) {
@@ -1640,8 +1687,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
       </>,
     );
 
-    Scheduler.unstable_advanceTime(500);
-    await advanceTimers(500);
+    await resolveText('B');
 
     expect(Scheduler).toHaveYielded(['Promise resolved [B]']);
 
@@ -1690,8 +1736,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
       'Effect [Loading...]',
     ]);
 
-    Scheduler.unstable_advanceTime(500);
-    await advanceTimers(500);
+    await resolveText('B2');
 
     expect(Scheduler).toHaveYielded(['Promise resolved [B2]']);
 
@@ -2068,8 +2113,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     await ReactNoop.act(async () => show(true));
 
     expect(Scheduler).toHaveYielded(['Suspend! [A]']);
-    Scheduler.unstable_advanceTime(100);
-    await advanceTimers(100);
+    await resolveText('A');
 
     expect(Scheduler).toHaveYielded(['Promise resolved [A]']);
   });
@@ -2094,8 +2138,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
     await ReactNoop.act(async () => _setShow(true));
 
     expect(Scheduler).toHaveYielded(['Suspend! [A]']);
-    Scheduler.unstable_advanceTime(100);
-    await advanceTimers(100);
+    await resolveText('A');
 
     expect(Scheduler).toHaveYielded(['Promise resolved [A]']);
   });
@@ -2829,6 +2872,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
       foo.setState({suspend: false});
     });
 
+    expect(Scheduler).toHaveYielded(['Foo']);
     expect(root).toMatchRenderedOutput(<span prop="Foo" />);
   });
 
@@ -2944,4 +2988,276 @@ describe('ReactSuspenseWithNoopRenderer', () => {
       </>,
     );
   });
+
+  it(
+    'multiple updates originating inside a Suspense boundary at different ' +
+      'priority levels are not dropped',
+    async () => {
+      const {useState} = React;
+      const root = ReactNoop.createRoot();
+
+      function Parent() {
+        return (
+          <>
+            <Suspense fallback={<Text text="Loading..." />}>
+              <Child />
+            </Suspense>
+          </>
+        );
+      }
+
+      let setText;
+      function Child() {
+        const [text, _setText] = useState('A');
+        setText = _setText;
+        return <AsyncText text={text} />;
+      }
+
+      await resolveText('A');
+      await ReactNoop.act(async () => {
+        root.render(<Parent />);
+      });
+      expect(Scheduler).toHaveYielded(['A']);
+      expect(root).toMatchRenderedOutput(<span prop="A" />);
+
+      await ReactNoop.act(async () => {
+        // Schedule two updates that originate inside the Suspense boundary.
+        // The first one causes the boundary to suspend. The second one is at
+        // lower priority and unsuspends the tree.
+        ReactNoop.discreteUpdates(() => {
+          setText('B');
+        });
+        // Update to a value that has already resolved
+        await resolveText('C');
+        setText('C');
+      });
+      expect(Scheduler).toHaveYielded([
+        // First we attempt the high pri update. It suspends.
+        'Suspend! [B]',
+        'Loading...',
+        // Then we attempt the low pri update, which finishes successfully.
+        'C',
+      ]);
+      expect(root).toMatchRenderedOutput(<span prop="C" />);
+    },
+  );
+
+  it(
+    'multiple updates originating inside a Suspense boundary at different ' +
+      'priority levels are not dropped, including Idle updates',
+    async () => {
+      const {useState} = React;
+      const root = ReactNoop.createRoot();
+
+      function Parent() {
+        return (
+          <>
+            <Suspense fallback={<Text text="Loading..." />}>
+              <Child />
+            </Suspense>
+          </>
+        );
+      }
+
+      let setText;
+      function Child() {
+        const [text, _setText] = useState('A');
+        setText = _setText;
+        return <AsyncText text={text} />;
+      }
+
+      await resolveText('A');
+      await ReactNoop.act(async () => {
+        root.render(<Parent />);
+      });
+      expect(Scheduler).toHaveYielded(['A']);
+      expect(root).toMatchRenderedOutput(<span prop="A" />);
+
+      await ReactNoop.act(async () => {
+        // Schedule two updates that originate inside the Suspense boundary.
+        // The first one causes the boundary to suspend. The second one is at
+        // lower priority and unsuspends it by hiding the async component.
+        setText('B');
+
+        await resolveText('C');
+        Scheduler.unstable_runWithPriority(
+          Scheduler.unstable_IdlePriority,
+          () => {
+            setText('C');
+          },
+        );
+      });
+      expect(Scheduler).toHaveYielded([
+        // First we attempt the high pri update. It suspends.
+        'Suspend! [B]',
+        'Loading...',
+      ]);
+
+      // Commit the placeholder to unblock the Idle update.
+      await advanceTimers(250);
+      expect(root).toMatchRenderedOutput(
+        <>
+          <span hidden={true} prop="A" />
+          <span prop="Loading..." />
+        </>,
+      );
+
+      // Now flush the remaining work. The Idle update successfully finishes.
+      expect(Scheduler).toFlushAndYield(['C']);
+      expect(root).toMatchRenderedOutput(<span prop="C" />);
+    },
+  );
+
+  it(
+    'fallback component can update itself even after a high pri update to ' +
+      'the primary tree suspends',
+    async () => {
+      const {useState} = React;
+      const root = ReactNoop.createRoot();
+
+      let setAppText;
+      function App() {
+        const [text, _setText] = useState('A');
+        setAppText = _setText;
+        return (
+          <>
+            <Suspense fallback={<Fallback />}>
+              <AsyncText text={text} />
+            </Suspense>
+          </>
+        );
+      }
+
+      let setFallbackText;
+      function Fallback() {
+        const [text, _setText] = useState('Loading...');
+        setFallbackText = _setText;
+        return <Text text={text} />;
+      }
+
+      // Resolve the initial tree
+      await resolveText('A');
+      await ReactNoop.act(async () => {
+        root.render(<App />);
+      });
+      expect(Scheduler).toHaveYielded(['A']);
+      expect(root).toMatchRenderedOutput(<span prop="A" />);
+
+      // Schedule an update inside the Suspense boundary that suspends.
+      await ReactNoop.act(async () => {
+        setAppText('B');
+      });
+      expect(Scheduler).toHaveYielded(['Suspend! [B]', 'Loading...']);
+      // Commit the placeholder
+      await advanceTimers(250);
+      expect(root).toMatchRenderedOutput(
+        <>
+          <span hidden={true} prop="A" />
+          <span prop="Loading..." />
+        </>,
+      );
+
+      // Schedule a high pri update on the boundary, and a lower pri update
+      // on the fallback. We're testing to make sure the fallback can still
+      // update even though the primary tree is suspended.
+      await ReactNoop.act(async () => {
+        ReactNoop.discreteUpdates(() => {
+          setAppText('C');
+        });
+        setFallbackText('Still loading...');
+      });
+
+      expect(Scheduler).toHaveYielded([
+        // First try to update the suspended tree. It's still suspended.
+        'Suspend! [C]',
+        'Loading...',
+        // Then complete the update to the fallback.
+        'Still loading...',
+      ]);
+      expect(root).toMatchRenderedOutput(
+        <>
+          <span hidden={true} prop="A" />
+          <span prop="Still loading..." />
+        </>,
+      );
+    },
+  );
+
+  it(
+    'regression: primary fragment fiber is not always part of setState ' +
+      'return path',
+    async () => {
+      // Reproduces a bug where updates inside a suspended tree are dropped
+      // because the fragment fiber we insert to wrap the hidden children is not
+      // part of the return path, so it doesn't get marked during setState.
+      const {useState} = React;
+      const root = ReactNoop.createRoot();
+
+      function Parent() {
+        return (
+          <>
+            <Suspense fallback={<Text text="Loading..." />}>
+              <Child />
+            </Suspense>
+          </>
+        );
+      }
+
+      let setText;
+      function Child() {
+        const [text, _setText] = useState('A');
+        setText = _setText;
+        return <AsyncText text={text} />;
+      }
+
+      // Mount an initial tree. Resolve A so that it doesn't suspend.
+      await resolveText('A');
+      await ReactNoop.act(async () => {
+        root.render(<Parent />);
+      });
+      expect(Scheduler).toHaveYielded(['A']);
+      // At this point, the setState return path follows current fiber.
+      expect(root).toMatchRenderedOutput(<span prop="A" />);
+
+      // Schedule another update. This will "flip" the alternate pairs.
+      await resolveText('B');
+      await ReactNoop.act(async () => {
+        setText('B');
+      });
+      expect(Scheduler).toHaveYielded(['B']);
+      // Now the setState return path follows the *alternate* fiber.
+      expect(root).toMatchRenderedOutput(<span prop="B" />);
+
+      // Schedule another update. This time, we'll suspend.
+      await ReactNoop.act(async () => {
+        setText('C');
+      });
+      expect(Scheduler).toHaveYielded(['Suspend! [C]', 'Loading...']);
+
+      // Commit. This will insert a fragment fiber to wrap around the component
+      // that triggered the update.
+      await ReactNoop.act(async () => {
+        await advanceTimers(250);
+      });
+      // The fragment fiber is part of the current tree, but the setState return
+      // path still follows the alternate path. That means the fragment fiber is
+      // not part of the return path.
+      expect(root).toMatchRenderedOutput(
+        <>
+          <span hidden={true} prop="B" />
+          <span prop="Loading..." />
+        </>,
+      );
+
+      // Update again. This should unsuspend the tree.
+      await resolveText('D');
+      await ReactNoop.act(async () => {
+        setText('D');
+      });
+      // Even though the fragment fiber is not part of the return path, we should
+      // be able to finish rendering.
+      expect(Scheduler).toHaveYielded(['D']);
+      expect(root).toMatchRenderedOutput(<span prop="D" />);
+    },
+  );
 });