Nothing like three people quitting on turn 1 when you are the cat. I somehow ended up finishing 2nd while getting pretty mediocre cards from my opponents.
Had the same problem just a few minutes ago.
Found a workaround. I had the error on Heroic, so I started up a Normal run and played a few games. I then went back to my Heroic run and it swapped my Heroic Mage deck for my Normal Hunter deck, I played 1 game and won, then it said I was defeated playing as Shaman. At least it's fixed now.
Finished 11-3 with Mage in Arena (was 11-1 at the final boss). I faced 7 Warlocks in-a-row (9 out of 14 overall were against Warlock), apparently there are no other classes to play against in Arena. I thought I played well but I just couldn't match the Warlock hero power and my opponent constantly top decking cards like Fungalmancer, Bone Mare & Demonbolt. My 11-3 streak continues, I believe in the last few months I'm 0-5 against the final boss.
I encountered a weird glitch. I used Moat Lurker on my opponent's Volcanosaur (Windfury + Divine Shield). A few turns later opponent killed my Moat Lurker with Kobold Illusionist and the Volcanosaur never respawned, it just left an vacant space on the board for the rest of the game. I assume my opponent saw the same thing since they never used it.