As best as I can determine, every single category got emptied of contents at some point during or after the hour or so of technical support work on the wiki in the middle of the day yesterday. If a page has been edited since then, it's back in all its categories, but everything else is still missing.
Case in point: The number one category on the "Most Linked Categories" special page is Images imported from TV Tropes without an identified license, which is supposed to have 49,176 members. But if you go there right now, there are three images in it.
I see no tools available to me to regenerate category memberships -- is this something someone else has access to? Or do we need to do something more drastic?