Having watched some people play it, it seems it's a common browser optimisation problem, Chrome fragments resource intensive operations sadly, I think I went overboard on the amount of enemies spawned and should have done more testing
Firefox seems to not have as much of a problem but now I know to check the other browsers next time!
Thanks for playing and for good feedback! The gun totally sucks and the wall collision hitbox is too big I agree haha!
Again, loved the hell out of your game. It's my favourite of the 18 I've played!