It’s happening randomly. It doesn’t happen when there are less than 5 people on the server. Any more than that and the game is unplayable. It just happened to me 4 times within 45 minutes between 4:30pm and 5:15pm CST. The avatar will fall through whatever floor / foundation / roof it’s on all the way down to ground level. Then it’s stuck in the building piece. You have to die or tear down part of the building to get out. If the foundation is only 1 block deep the avatar will only be stuck to their waste. However, if the foundation is deeper, the avatar falls all the way down to the ground.