I am on a Nintendo Switch. I select the pencil icon beside my realm to open my realm settings, select "Game", then "Replace World", choose which world I want replace my realm with, and every time I try it says "An error occurred" and "Level export failed". I've even tried again after about 15 hours, and I still get the same results.
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Thank you for your report!
We're tracking this issue in REALMS-474, so this ticket is being resolved and linked as a duplicate.
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