I'm guessing the game ends like a regular game would just for no reason, right? If it's ending like that it's probably cheat detection. Whenever I've used cheat engine on it ends the game, so on these ones you can't do those stuff. Your friend was probably using some, if it's not that then you should probably dm the map maker since there might be some running program of yours that triggers it.

I'm hosting it on a plutonium server. No clue if that causes interference or not, but it works fine in solo.

This is probably a feature I completely overlooked, but why do maps end early? I was on like round 13 and me and my friend were both still alive and the game just ended in the middle of a round. Am I missing something?