"gitlab-generated" .gitattributes random behavior

We are experiencing weird issues when using gitlab-generated attribute in .gitattributes.

This is best illustrated by Gitlab's own repository:

gitlab-com/runbooks!9492 (diffs)

You can see how some of "autogenerated" files are marked as generated, and some are not (in the screenshot, I collapsed it by hand, but you can see how the automatic note about generated file is missing).

That repo only has one rule:

**/autogenerated-*.yml gitlab-generated

We experience similar issue on a bigger scale (private repo on gitlab.com) - some folders are ignored , sometimes individual files, and it's hard to tell what's the pattern of this behavior.

We're pretty sure it's not a configuration issue on our end as testing git check-attr returns 'gitlab-generated: set' for files that Gitlab fails to mark.