Hi guys, sorry — I could have sworn I had updated this, but just realized I hadn't. It turns out, our database was split on the same day our host migrated their cPanel to a new platform. We were seeing two databases, with one reading 0kb, so we assumed it was a weird empty duplicate. Turns out, not. All the posts from the last ten months were in there.
We just re-ran the converter on that database, deleted duplicate threads, and all is well now!