On September 22 around 12:30 AM I went onto my Minecraft World on Xbox One this world was a Superflat City that I started 5 years ago and when I logged on almost all the world was a Void except parts of mountains and tops of sky scrappers. I believe what happened was that in the most recent update the world block heights was changed and in doing so the void was raised. This was an old Superflat from the Xbox One edition that I brought onto the new Minecraft so it went down 29 blocks unlike most Superflat worlds that go down to 3. I really hope that there is a fix for this because me and my friends have spent so much time working on this world and just for it to be practically erased is disheartening.