TypeError: Cannot create property 'headers' on string 'Cannot merge user ekqdqzv5w into itself!'

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View details in Rollbar: https://rollbar.com/freezy/server/items/32/

TypeError: Cannot create property 'headers' on string 'Cannot merge user ekqdqzv5w into itself!'
  File "/var/www/server/production/v3.0.11/node_modules/@koa/cors/index.js", line 97, in next.catch.err
            err.headers = Object.assign({}, errHeadersSet, headersSet, {vary: varyWithOrigin});
  File "/var/www/server/production/v3.0.11/node_modules/async-listener/index.js", line 504, in Promise.propagateAslWrapper
          nextResult = fn.call(ctx, result);
  File "/var/www/server/production/v3.0.11/node_modules/async-listener/glue.js", line 188, in Promise.__asl_wrapper
          var returned = original.apply(this, arguments);
  File "/var/www/server/production/v3.0.11/node_modules/async-listener/index.js", line 529, in proxyWrapper
              return next.__asl_wrapper(ctx, fn, val, last);
  File "/var/www/server/production/v3.0.11/node_modules/async-listener/index.js", line 541, in <unknown>
              var result = (promise.__asl_wrapper || propagateAslWrapper)(this, fn, val, next);
  File "/var/www/server/production/v3.0.11/node_modules/async-listener/glue.js", line 188, in <unknown>
          var returned = original.apply(this, arguments);
  File "<anonymous>", line unknown, in <unknown>
  File "internal/process/next_tick.js", line 229, in process._tickDomainCallback [as _tickCallback]