Alrighty! I took a look at the debug data you sent. Not sure how it happened, but it seems somehow that achievement value became null. Here are some steps to get it back in a good state:
1. Go to %appdata%\Godot\app_userdata\Decks Out
2. Open metagame.save in a text editor
3. Change the achievements value for "OtterFavorite" to 0