@DunkelBlume Very glad to hear, thanks for letting us know!

@DunkelBlume Thanks for the additional info. Noticing the commented-out line:

// Default skin hold the hoodie hole, laces and the eyes
// newSkin.AddSkin(introvertSkeletonData.FindSkin(CharacterCustomizationSkinsPrefixes.defaultSkin));

If you repack the skin to a single atlas texture, you would want to add the default skin as well. Note that there is no need to call FindSkin for the default skin. Unless CharacterCustomizationSkinsPrefixes.defaultSkin is something special, you can just use:
newSkin.AddSkin(introvertSkeletonData.DefaultSkin);
If you don't repack the skin, you can omit the line as the default skin is already automatically "added" to the skeleton.

My following questions from my posting above remain:
How is your problematic skeleton instantiated? Is it instantiated programmatically, and if so, how?
Is it destroyed when you unload your level and switch to the lobby?
Or is the skeleton loaded as fixed part of the scene?