Failing to sync

So basically what has happened is ever since October 5, my friend and I's 4 year country world has been having the "out of data storage" issue and then some corruption issues. I contacted Minecraft Support and they helped a bit but we were still experiencing issues. One of the suggestions was to reset the Xbox but keep games and apps and then resync the world when reset. We've just tried to resync it and it took about 20 minutes to get to 100% and then it said failed to sync.