World got shifted 40 blocks up

So, I was loading into a Minecraft world I've been playing on for some time. it's a flat world where I use to create things. I load up the world it was completely empty At first I though maybe I flew very high up to do some king of experiment but when I turned on the coordinates I found out the I was quite close to the ground. Luckily before this new beta version I created a lv 3 map of everything in this world. so I filled in a block of stone in the air placed down a ender chest to get my map and looked at the map. It seemed like every chunk I rendered in got turned to air. I though maybe it was just a visual thing. I reload the world and still nope nothing loaded. Then I decided to fly around a bit to figure things out. I found parts of skycrapers that I made and they were only the top half of the builds. At this point I knew something happened to how Minecraft worlds generate. It seems as if the world was shifted 40 blocks up but non of the original blocks were moved up. Luckily I also found another Image of the same location a from before the update.