Everytime I enter one of my worlds the game immediately closes the world and gives me the message in the screenshot
Edit: I have over 5gb of storage space left
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Could you confirm which storage location you have chosen from the settings please?

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Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-37269 due to the more general or descriptive summary.
Your votes, additional information and observations are very useful, so if you can add them to the comments section of the parent issue it would be appreciated.
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I too am still getting this message, despite over 7 GB on Xbox One external hard drive. The only thing I can do is uninstall/reinstall, then it works for a couple times.