in the most recent beta, with the Caves And Cliffs experimental features, a bug arose in which I was inside a cave, exited the game, entered the world again and appeared on the surface. I was practically teleported to the surface.
MCPE-139712
[Experimental] Player teleported to surface when upgraded from 1.17.30.22 to 1.17.30.23
Resolved
Fixed
6
This happened to me too. Though, most notably, you only teleport if you are underground when exiting the game. If you are above the surface, you do not teleport at all.