Sorry to hear that, but I'm not able to repeat your bug. Could you tell me in which stage were you when it crashed? Were you controlling a spaceship or a tetris piece? The last part of the spaceship should be quite difficult, as it is designed to kill you eventually (it's an endless level), but a game over menu should appear when you die if you don't reach a certain threshold to pass to the next level. :(
The spaceship part has three stages, so you were in the final stage of the spaceship. When dying in the final stage, you should automatically appear on the first tetris level (tetris minitutorial). I still don't understand what happened within the code... I tried to replicate your bug, but it worked well for me on different tries with different browsers (Firefox, Chrome & Edge).
Either way, thanks for the reply!