I noticed that the Dressing Room has a button to add a custom classic skin. Clicking on it lets me browse to pick a .PNG, much like on PC. But once you click on the image file, nothing happens. This has been tried both with skins on flash drives as well as skins transferred to the Xbox’s Pictures folder.
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Thank you for your report!
We're tracking this issue in MCPE-152259, so this ticket is being resolved and linked as a duplicate.
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It happened me a while ago... It is caused due to lack of internet.