Great game! Great idea, but sometimes it works not pretty well. But I think I never would have guessed this idea!
Viewing post in Don't Trust the Devs jam comments
Those blocks appear when you tried putting too much blocks in the scene.
You have a little counter under your life bar, and if you put too much blocks in the stage, the counter will turn red. When it is in this state, random block will become "ghost-blocks" which you will fall through !
Use the limited block quantity per level to prevent the glitchy blocks from appearing ;)