- Edited
Battern I don't really know the answer but one thought that immediately came to mind is that physics engines usually leave tiiiiiny gaps between or around objects. For example if you would zoom in far enough you could see a person float a couple of millimeters above the ground instead of standing exactly plane on the ground.
They do this to compensate for inaccurate floating point calculations and to prevent objects from overlapping. This could happen in the early days of physics engines where you would sometimes see an object getting catapulted away into the sky for no apparent reason. This could happen especially after spawning a new object or entering a level or reloading a savegame.
So maybe this is caused by this tiny gap. Hard to say without knowing what you do or how your code looks like.