I noticed this when I joined a survival world with my friend, CHOURRIOUS and there were large holes spread apart and when I told him, he said he didn't see them.  He could collide and I would fall into the void.  Then I joined another friends world and this time CHOURRIOUS could see them like I could except for the host.

So the host can't see these holes, but we can and if I try to walk further, I fall though the ground into the void.