Juda H

Same, even on the site NameMC it shows skins with slim selected wrong. Maybe "slim" is saved as "classic" when uploading a new skin?

I have the same issue as well.

After uploading a skin, it cakes up to 15 minutes for the skin to be seen online.
Also the character model of slim skins change to the Steve model. (When slim is selected when uploading a new skin.)