I found a problem that can crash the XBOX One and Win 10 Game Version when the World uploaded from PC to Realms and downloading on XBOX One.

Step:
1) Create a new World on MC Win 10
2) Upload the World to Realm Server
3) In XBOX One, Download the World from the Realm Server
4) Play the downloaded World on XBOX One (You can still play as Singleplayer)
5) When you're in the World with the XBOX One, Connect to the World (Friends (Network)) from MC Windows 10 with same Xbox Live Account.

The XBOX One Version crash first and then the Win 10 Edition
It crash when Realms is Open or Closed.

Edit: I think i found the problem.
You can not connect with same Xbox Live Account in same time to Realms Server (makes sense) but if you Download the World to Xbox or PC and play in Multiplayer local Network and connect with same XBOX Live Account (Xbox One and Windows 10), the Game have conflict with 2 Players with same Xbox Live Account. I can still play in local network with two Xbox Live Account when the World is not uploaded/downloaded from Realms Server but if the World is downloaded from Realms server, i can not play the World anymore with same accounts in local Network and the result is XBOX One Game crash and Windows 10 Edition too. I think this is unintentional and has not been considered in the development? or is that wanted i can play local Multiplayer with one XBOX Live Account on XBOX One and Win 10 Edition in same World and same time