Just as the title says. I was teleported to the Nether Roof by an arm in the snow on Galifrey. It should be noted that I was actually teleported with my lower half in the top layer of the bedrock. I'm not a coder or anything but I recommend that if the player is being sent to the nether then it can't be with a Y level over 120 (not sure if that's easy to do, also not trying to tell you how to do your job, just a suggestion). I'm going to go find a way to get down now, thanks for looking at this.
latest.log

Will be fixed next update. You'll need to use creative to dig down in the mean time.

Fixed in latest 1.16.2 and latest 1.14.4