Hey thanks so much for reporting the lag and freezing issues. Do you remember around when the lag started to happen? Trying to investigate this the best I can, as I am developing on Mac.
Yeah, I really do want level 20 to be a continuous long level, since it gives you a bit of variety in the pacing. That's very strange though, that the Newgrounds version didn't freeze. Especially if it's the same build version.
FYI, I've been able to reproduce the game crashing/freezing. Seems to happen when you let the game run for a while. Will post an update when I find a fix. Keep you posted.