Imported custom PNG skin reverts to default after closing and reopening the game on Windows Bedrock

Platform: Windows PC (Microsoft Store Minecraft Bedrock Edition)
Game Version: 26.51

Steps to reproduce:
1. Open Dressing Room, import a local PNG custom classic skin.
2. Apply the skin and save the character. The skin shows correctly right away.
3. Close Minecraft, wait several hours, then launch the game again.

Expected result: The custom skin stays applied.
Actual result: The skin automatically reverts back to default Steve/Alex.

Additional information:
- Only manually imported PNG skins have this problem. Marketplace skins work fine and do not reset.
- I only use this single Windows PC, no other devices logged into this Microsoft account.
- No manual reset was done by me. It happens automatically after game restart.