I have this same issue

I've been playing this game with the launcher for a while at medium settings and I've rarely run into fps drops or anything like that, then today I start the launcher (Nothing running in the background) and it runs fine until I load into the map. INSTANT drop all the way to thirty. All my drivers are updated, I've tried turning the graphics setting down, locking my fps in the console, turning off sync all frames and locking it to 60, setting the game to run on dedicated gpu, etc. Nothing has worked except reinstalling the game (I've had this problem before a while ago) but I want to look for a more permanent/easier solution.
(edit: Multiplayer works fine now, just zombies is having issues)