There seem to be two bug:
1.
If my towers kill all enemy units visble on the field before the next unit spawns at tne start of the way, then the enemy units won´t spawn anymore but the game continues endlessly to run as if the enemy wave is going on.
And then you have to restart the whole level.
2.
If you finish a level but click on "main menu" instead of "next level" you will be taken to main menu and see your stars on the completed level but the next level won´t be opened. So you have to play the level you just finished successfully again.