Plutonium

Fixed by reinstalling Plutonium, tried reinstalling the game before that

I port forwarded and have been hosting for a couple days, everything smooth.

I tried one mod with one friend, we both installed and it worked. It was the Nuketown mars map.

Cut to today, installed zombie counter, mod menu, and share your perk. My game wouldn't launch after installing, deleted the mod menu and it fixed that. Unfortunately friends were unable to join.

Had them install the mods, it didn't work. We all deleted the mods, still they can't join me.

I've tried restarting my PC. Closing/reopening party type. Turned off firewall, added port exceptions to firewall. Not sure why this broke it but we're no longer able to play together. Would appreciate any help.