When I logged off in an End City for about 2 minutes, trying to log back on would get me stuck on an endless "Generating World" loading screen. I have created a copy of the world, changed simulation distance on settings, and even tried to let it load for about 30 minutes and nothing has happened. I do not have realms and cannot load a previous save, and I cannot have a friend load up the chunks around me as they cannot join if I am not in the server.
Edit: I started a free 30 day trial for realm and I was able to get a friend to load the chunks around me. I was then able to join.
Thank you for your report!
We're actually already tracking this issue at MCPE-49778, so we will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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