It's a good start to figure it out. I have some idea, so I try to reproduce the bug. Thank you for the feedback! :)
May that can help if you tell me, this bug appeared for you on the 1st or at the 2nd level too?
A couple more things I noticed. Sometimes when moving the block didn't work, it seemed to shudder a little, like it was stuck. And sometimes when it didn't move, if I then tried to move forward, the block would then move. Perhaps because I had moved... Best of luck with your game!