Wow that is hypnotic.
But anyways, yes, I recognize this! Things fall through the floor if the velocity keeps increasing by gravity even when the object has already landed on the floor, so when the "velocity" is a bigger number then the floor is deep, the collision checking only check if the space under the floor is empty and goes there.
You can draw this on sceen with this in the Cricle.gd and calling update() on the process function:
draw_line( Vector2.ZERO, velocity, Color.beige)