A friend and I played up to wave 10 on normal difficulty. By the time we'd hit wave 10, there were monsters everywhere and it was total chaos. We were having a great time.
We continued playing today on wave 11, normal difficulty (this was pre-selected on the lobby screen) and for some reason it was a complete joke, there were barely any monsters and it wasn't fun at all.
Any idea why the difficulty just completely went to zero after restarting?