A person

Last time we got this bug it was because Bluehost's Varnish caching system didn't play well with our forum software, so disabling the server side caching on the hosts end did the trick.  So I'm HOPING this is just happening because Bluehost is trying to deal with a ton of holiday traffic.

Aaand yep.  I checked the host, and it looks like Bluehost had an issue a couple days ago that must've reset our caching back to on.  So I turned it back off, cleared the cache on the server side, cleared the forums cache, and it looks like we're back to normal.