Actually ended up figuring it out, in %localappdata%/Plutonium/storage/t4/players/$$$ the game stores what looks like config files for every custom map that has been loaded on the client. At some point they must have gotten corrupted, as custom maps started working just fine after deleting them and letting the game auto-generate them again.

Having an issue that's stumping me pretty bad, every single time I try to load a custom zombies map my entire game window fails to load when the game restarts. The application still appears in my taskbar with a generic icon but there is no audio or visual at all, and must be closed via task manager. Not getting errors in console or anything, as far as its concerned the game is running fine. Just earlier today it was able to load custom maps completely fine so I seriously don't get what happened.

I'm running the game in borderless mode if that helps