Aaaand the problem is back. I'm back down to the same three options from my earliest posts when I try to filter. Frustratingly, this includes the 2014 Monster Manual content, which I'd already disabled. And WOW, I wish I could edit the title of this thread. I didn't even understand the problem's scope when I posted it. I'll go clear my Roll20 cache, but I'm not sanguine about this working given I had the problem, then didn't, until now.