I have auto next level (hotkey G) enabled.
During the level I press the left cursor key to go back to the previous level. But, because auto next level is on, immediately the level goes to the next again.

Now the game doesn't work anymore. Crusaders are invisible and the enemies walk towards you until the end (left side) of the level. Now they continue to walk off of the left side of the screen and the whole game stutters and becomes very slow and sluggish.

Then the game doesn't respond anymore. I have to close the game and restart.

This happens a couple of times a day for me. GGGGGGGGGRRRRRRRRRRRR

Steam v0.83 (but older versions also had the problem).
Windows 10 x64

Also happens on IE and Chrome (playing through Kong).

(Have had it several times - jumping back a level to get the few necessary seconds to change formations and such, or just to reset the formation because part had been killed due to my leveling up just a bit too late.)