Thanks for playing. Unfortunately, the 4th level isn't a bug. It is just poor playtesting. The difficulty spikes quite rapidly. At the 4th level, you are probably missing the snare on the 3rd note of the 3rd beat (in the same column as the second hi-hat). I was playing with the idea that the replay would cost some points, so it would also be interesting mechanics, but I decided not to overcomplicate it. Thanks for the feedback!