Did you try waiting for a while?
Try clearing the cache:
- press and hold the Xbox button on the front of the console for 10 seconds until it shuts down
- unplug the power cable and wait 30 seconds
- plug the console back in and turn it on
I don't suppose you have access to a different Xbox, that you can log into your account on, let it sync online saves and then test if this still happens?
