You may see some variation of the above error or infinite loading screens, corrupt screens, etc
Fully update your game. If you have multiple folders inside of LocalData (which is a folder inside of your Master Duel folder), you need to make sure they are ALL updated or delete the ones which aren't updated.
- To update your game you need to go the home screen of the game using Steam. The home screen is the screen where it shows your duelist name and level in the top left of the screen.
- Support is not provided beyond these instructions as these are the only known ways of fixing these issues.