world does not sync

When syncing my world from xbox one to the beta (if the game doesnt crash and actually lets me play my world) my settlement changes to a complete new biome and my whole builds are completely gone. I have tried going to another place on the world and saving it on the xbox one, then syncing it again. I then go back to the settlement I built as it shows it on the map just for it to be this biome which has now appeared in its place. I did the same process but started in the nether; this was a bad mistake as when I loaded in I fell through the map and straight into lava.

Im not sure if this is because its quite a big world i have explored (25x25 map) and i have not anything like redstone builds here so couldnt be that.

This is only part of the issue as if i do load into it the game crashes and i have to do a hard reset of the console just for it to work again.