Came to report this bug and it was literally reported in 2019. Still not fixed.
When selecting a skin for the deck during deck building and not leaving it to random/favorites, the skin will reset EVERY. SINGLE. TIME you close the game.
This makes it impossible to use different skins for specific decks.
Delete the affected deck and recreate it. That fixes it for me.
It doesn’t for me. Whether I build a deck manually or copy a code. Relogging resets the skin to random. Only the skin, card back and coin are fine.