Didnt get a chance to post this earlier, when u hit wave 40+ it gets very laggy. I think its because there is so many ships on map because it clears up when u start killing them. There really isnt much u can do when its that laggy cant even see weapons hitting other ships. Pretty much just gotta sit there and hope ur ships live.
Edit: When u finish a wave 40+ it kicks u out of game but thankfully it still saves ur exp and money earned.