Board Thread:Support Requests - Getting Technical/@comment-5785681-20190322090649/@comment-24931587-20190325172000

The problem is in Template:Character Navigation. The categories were added to that template 5 years ago, so the problem might not have become apparent until a cache was flushed or pages using the template were edited.

It's strange that you can't edit the template since you're an admin, and apparently locked it yourself a few months ago. If you go to Special:ProtectedPages, you should be able to change the protection level for that template so you can fix it.