unable to upload world to Mojang as part of Beta program 1.2.3

I am trying to upload a world to Mojang as requested.

The upload starts but stops at a random time and crashes the game, game goes back to XBOX homescreen when the issue occurs.

I have tried 4 times, stops at random times, furthest i have got is 40%.

Note: I am trying to upload as i am experiencing the Parts of maps missing issue.