Nope, I've only got one GTA folder. I don't do multiplayer, so I didn't bother trying to keep Online working. My game isn't installed on the C: drive, but at "D:\Steam\steamapps\common\Grand Theft Auto V" instead. Maybe I'll reinstall the game on the C: drive and see if that makes a difference.

edit: wt actual f, that actually fixed it....

Don't install GTA V on non-C drives, I guess.