I have been experiencing this issue for about a month. Every time I set a custom skin, I can only have it on until I close the game. It always resets to default when I open the game back up. At first it said my skin wasn't compatible with multi-player, but now it just goes back to default. I don't mind it much, but it gets annoying having to keep resetting my skin.
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Thank you for your report! However, this issue has already been reported as MCPE-32089 and as such, will be closed as a duplicate. As a reminder, please search for an issue before creating a new ticket for it. Have a great day! 🙂