I have an extended deck and I don't get an error about the cards. But whenever I try to start a new match it just cycles the counter for a bit and then comes back saying no opponent found. This has been ongoing since last night. I can't imagine that I've been unable to find an opponent for over 8 hours straight without something actively preventing me.
People use 2'nd tier mostly. That's 24stars - 31stars if im not mistaken.