I was syncing up my world that is about 210 mb so since it would sync properly after many different numbers like 250 mb, 700 mb, or 820 mb, I would go into someones world to restart the sync I guess to later exit but when I joined my friends world, it instead put me inside of the world I tried syncing and it was chunks of jungle where used to be an area that I and a few friends built on. About 60% of the world became what the world used to look. Everything I worked on was gone. I really hope this gets resolved. You could allow people to save their work on the hard drive of the Xbox instead on a cloud.