I haven't seen this myself, but I have heard reports from multiple people that the "there are unreviewed changes on your watchlist" message sometimes appears, and stays visible for a long time, when there are actually no such changes (checked through the filter on Special:OldReviewedPages, so the reason cannot be merely that the changes are too old to show up on the watchlist). This can be somewhat annoying as this message is designed to be prominent.

If it is any help, I can ask someone to supply exact time and contents of their watchlist in private next time the bug appears.

Version: unspecified
Severity: minor