Last modified: 2008-08-04 20:48:22 UTC
Items will sporadically fail to show in large (several dozen or more items) watchlists. This error occurs across a wide number of versions, across a variety of installations and notably occurs in ver. 1.14-svn on Wikipedia. It occurs primarily for project space pages in older versions and seems to occur more evenly across namespaces in more recent versions (though this may simply be a random fluke and not indicative of the error). With even larger watchlists (several hundred or more items) several items can fail to show at once. Unwatching and rewatching the page(s) in question has no effect on the error. The error goes back to at least ver. 1.7.0 and has been experienced on private installations, the English Wikipedia and Wikia installations.
This is pretty vague, but I'd probably attribute most of this generally described phenomenon to bug 5546 (logged actions such as renames, protections etc would often cause things not to display in the watchlist), which was fixed a while ago.
If you can duplicate the problem on Wikipedia currently, please try to describe an instance in as much detail as possible (exact title, time, screen shots, comparisons of showing and non-showing displays, etc).
*** This bug has been marked as a duplicate of bug 5546 ***