I've been seeing a growing number of complaints about the enemies on Level 4 being invincible, so I've taken a look at them and found what was causing the bug. After testing it out, I can say that the bug should be taken care of. Sorry for not taking care of this sooner!
And about that break I mentioned a few days ago, I'll still be taking it because of a personal situation that's been keeping me busy. I'll be able to work on little things here and there, but I won't be able to spend more time until next week. I hope you understand.