We recently noticed that reviewdog was no longer capturing output from remark-lint, here is a comparison:

• https://github.com/CivicActions/guidebook/runs/22855557650 (pipeline logs https://github.com/CivicActions/guidebook/actions/runs/8350023946/job/22855536851?pr=1099)
• https://github.com/CivicActions/accessibility/runs/22680298230 (https://github.com/CivicActions/accessibility/actions/runs/8287582863/job/22680270978?pr=741)

I tracked down the issue and it is because the output of remark lint was adjusted last year in vfile/vfile-reporter@f987b52 (and you can see the changes in the documentation here remarkjs/remark@6a43da8#diff-1152eab75d1ca2f7af44b54d8655b0cc01168ea48f5f9de4b346acc526eefb28L155-L160). Most of the whitespace changes is not a big deal but removing the two spaces between warning (or error) and the message causes a failure to match the format. Here is an example of the just that change:

 resources/markdown/README.md
-  25:3  warning  Incorrect list-item indent: add 2 spaces  list-item-indent  remark-lint
+  25:3  warning Incorrect list-item indent: add 2 spaces  list-item-indent  remark-lint

I believe the format in https://github.com/reviewdog/errorformat/blob/master/fmts/markdown.go#L10-L11 needs to drop the extra space to match the changes. I will try to share a pull request to make that change.