I am not sure what the circumstances are for this to occur exactly. I do have an example here:
This Wiki uses version 1.18.1. For some reason, when the user presses "next200", it does not go to the next 200. The link changes, but the page doesn't. If you change the pagefrom to just from, it works fine.
This could be one of two things.
1: *All* of the pages in that category have a sort key on them.
2: The use of a "/" in the page name, which may be rather unorthodox.
If it is #1, then this is an actual bug in MediaWiki; sort keys shouldn't break next/prev category pages. If it is #2, I can fix that with some bots.