this issue occurred for me through synchronization between the Android and Nintendo switch versions of the game using the same account.

on the Nintendo switch I have platform-restricted skins, which understandably can't be used on Android.

the game however does attempt to sync this skin, resulting in an error on the Android version every time the character selection screen is opened.

imported skins on Android cannot be synchronized to the Nintendo switch either and cause loading problems as well, but this causes issues that are more unpredictable.

I've had the skin/character appear as invisible or as Alex in the character select screen on the Nintendo switch, and after returning to android this character would either be restored to the imported skin, be replaced with Steve, or be deleted altogether.

I think a solution would be to prevent the downloading(and overwriting) of incompatible characters/skins, and keeping "last used skin" synchronization locked to the platform.

or alternatively separate skin-pack skins and imported skins from the new custom character system, and simply don't synchronize the "active" skin/character if an imported or skin-pack skin is in use.