The playlists were built using my existing library, some as recently as a few months ago.
Rescanning the Library folder doesn't find anything new, and the issue remains after doing a rescan of all files.
I just sent all playlist files to my Library, and now none of the files in one of said playlists can be found even though they're in my Library, which is
exactly the issue I had in February that is probably behind all of this. I also noticed at least one file in a different playlist that is still not in the Library and now it's not even in the playlist it was just in anymore.
I'm sort of thinking I should just start from scratch.