Update: It was Cyclic. Looks like people have also encountered the same problem as me and reported it to Lothrazar's GitHub already, so hopefully it'll get patched out soon.
that solves it! i tried disabling only one of them and BOP froze my game while Terralith crashed once again and threw another exception with RegionsUnexplored.
i'm trying the biome mods on a fresh profile and it seems like they all work together, so it's probably a different mod that's causing the crash...
https://pastebin.com/25pqvLb5
I don't know why it's crashing, I don't think I have any conflicts or out-of-date mods (outside of a few datapacks). I also tried it with the beta versions of Quark removed and the previously mentioned datapacks disabled (https://pastebin.com/F1G0QFy4) and it was still a no-go.