I recently upgraded XWiki from an older version (I think it was 13.x) to 18.5.0.
Since the upgrade, the notifications button doesn’t seem to work correctly. The notification bell looks strange, and clicking it doesn’t display any notifications. Instead, it appears to load indefinitely.
Your problems might be completely different, but better be safe: after a XWiki upgrade, it’s possible for your browser to have cached and still serve you older versions of some pages. So make sure you do a hard refresh at least once (usually, Ctrl + Shift + R).