I had it happen in some places before the caves were in testing.

For me the ground would pop out of shape from how I leveled it but one hit with the hoe set it back. It was odd though. At first it would pop up or down then it seemed to settle down a bit and happen less often only dropping down.

Only one spot. But I don't normally do a lot of ground altering and typically work with it. In this case it was just an area on a hillside just above the back of a troll cave. Leveled it off to accommodate a kiln and furnace.