You were right! The slo-mo was the problem. Or rather that the game tried to increment some non-existent variable I forgot to wipe out. Somehow it didn't crash instantly, only after player's death. It also prevented activating the baddies on the level.
I'm glad you like it! Stay tuned for future updates if I get enough feedback on what to fix and/or come up with ideas for new features. BTW, there are boss enemies every 20 levels, be sure to check them out! They may not be the most sophisticated and difficult ones, but I think it's a nice break from the usual baddies :)