I had a world with about 3 months of build time invested. For whatever reason, the save for this world became corrupted during sync in the cloud (no, I didn't cancel or power down during a sync).  

The world was not corrupt in local storage, and I could continue to play offline on my Microsoft account.  However, the following scenarios occurred that prevented Minecraft from normal network play on my Xbox One.

1/ If I was signed in and launched Minecraft, I would receive a sync error after the rotating splash.  Clicking cancel would see the splash rotate until I force quit Minecraft.

2/ If I was not signed in, I could launch Minecraft to home screen, and clicking play would get the sync error.  Clicking cancel here I could continue to play, but effectively the game was offline (so I could not invite people to my game).  Also, my "Realms" upsell and other network features were disabled.  I had the "Oops! Your Microsoft account is disconnected..."

3/ Following the Xbox reset instruction by microsoft, I lost my local storage and the game. One back, the world registered as 198M (where it was 108M on local storage). I could not recover this world, because it says its corrupt when re-loaded from cloud.

Note, my Xbox has amble physical storage, and cloud storage, available.

As a player, a single corrupt world in cloud storage should not interfere with the entire sync process.

As a player, a single corrupt world should not interfere with game launch or network game play (for new games).

As a player, I should have better error messages and diagnostics available to identify exactly which world is corrupt or mismatches between cloud and local storage. I should have the option of obliterating the corrupt cloud stored game and replacing it with the working world from local storage.

My corrupt world is still available in cloud and I can share my account details for you to figure out what is broken.