Skins keep resetting when joining servers

Short description of the issue

Custom uploaded skins and certain Marketplace skins (without 3D cosmetics) reset to a default skin upon joining a server. This issue has been persistent since version v26. Despite a clean reinstallation, the character model consistently reverts to a default skin in multiplayer environments.

Steps to reproduce the issue

1. Upload a custom skin from the local PC or select a Marketplace skin without restricted cosmetics.

2. Verify the skin is correctly displayed in the Main Menu/Dressing Room.

3. Join any multiplayer server.

4. Observe the skin change to a default character in-game.

5. Return to the Main Menu and observe the character preview.

Expected result

The chosen custom or Marketplace skin should remain active and visible to both the player and others while on the server and upon returning to the menu.

Actual result

The skin resets to a default skin (e.g., Steve or Alex) as soon as the server connection is established. After leaving the server, the Main Menu also shows a default skin, even though the Dressing Room still considers the custom skin "equipped."

Additional Notes

• This issue has been occurring consistently since version v26.

• Troubleshooting already performed: I have completely uninstalled Minecraft and manually deleted all associated folders in %TEMP% and %APPDATA% to ensure no corrupted cache remains.

• The issue persists regardless of the server joined.