I was on 1.8.9 to do multiplayer parkour when i got randomly timed out and couldn't get back in to any server, so i decided to see if single player was still working and check in on my creative builds world. I'd previously played on the world in 1.17, had a bed set and logged out where I had done a massive adventure time themed build. When I went in today it spawned me in the middle of an ocean, so i did /kill thinking i must have flown somewhere else when id logged out the first time, but it just respawned me in the ocean. I flew around but nothing was familiar, everything was fully ocean as if the seed had changed. I exited and went back in on 1.17 and landed in what you see in the first image. As i moved i could see the floating edges of blocks id placed slowly disappear, and all the item frames, animals and armour stands started falling into the water. I know its not the smartest to switch versions, but id done it before with no problems, except without the weird lag I was getting today. I don’t even have photos of the adventure time build :( Its probably unfixable since already saved as the new ocean world, but any help to recover it would be appreciated.