If connected to Wi-Fi, the game either just remains on the loading screen before entering or the menu screen if it manages to reach that stage. There is also no place to view your achievements. Unable to play Realms on mobile data.
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[Mod] Celesian
Thank you for your report!
However, this issue is a Duplicate of MCPE-61689.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
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Same thing.