So I just turned in a quest and the reward choices were freeze, 4800 coin, or an Eternal Warrior card. I have the warrior maxed out so I took the 4800 coin, the currently most precious commodity in the game.
After picking it I joined a 2v2 and got a pop up that an unexpected error occurred and the game reset and restarted. When I got back the coins were gone and the quest was no longer turned in. So I turned it in again and got 1000 gold as my best of 3 poor choices. I would be really upset if I needed that warrior card but as it is I want the coin back… I will submit a ticket as well but thought it was worth reporting the issue here on the forums.