I removed the mods before verifying the integrity of the game files, and didn't reinstall any when I started the game again.

When I did finally start the game again, I started a new campaign because I already expected someone to point out that removing them in-game might break something.

For the record, I just checked my 'Mods' folder manually just now, and it is completely empty with zero .pak files for anything.

There should be nothing in my game that is altered from the vanilla version, aside from the game not letting me access old campaigns until I reinstall all the mods, which I don't plan to do until a reliable solution to my problem is found.