I've tried checking my save files with Fallrim, it's all clean (as it should be, since I didn't add/remove any mod throughout the playthrough). Not too sure about having too many spells, I have less then 30 items on the list (spells, shouts, passives, etc). As for conflicts, MO2 shows absolutely 0 conflicting files between all the magic mods I use (okay, there's one, it's Arcanum replacing SKSE64's default spawnertask.pax, but that's it). As mentioned in my original post, the issue only appears once I've reached a certain (unknown) point in the game, so previous saves work just fine. I didn't try starting a new game (considering the bug only shows up at an undetermined point), but since I've moved everything from Vortex to MO2, the new character I made might as well count as a new game. With nothing left to try, I'll just remove most of the magic mods (or anything that adds entries into the magic menu like race or standing stone mods) I have installed and start a new game...hopefully, that's gonna help me avoid the problem for good.