Exact same thing happened to me. I played historic ranked I believe but historic none the less and during my game I completed the kill 25 of your opponent's creatures quest for 750 gold. Before my match, I had 650 gold and after my match ended and it popped up on my screen that I completed the quest and I had 3 rewards to collect. 1 was the 750 gold from the quest, 1 was an uncommon card called roiling regrowth, but I can't remember the third reward. I tapped the collect button and my gold amount never changed but I still received the card reward.
Exact same thing happened to me. I played historic ranked I believe but historic none the less and during my game I completed the kill 25 of your opponent's creatures quest for 750 gold. Before my match, I had 650 gold and after my match ended and it popped up on my screen that I completed the quest and I had 3 rewards to collect. 1 was the 750 gold from the quest, 1 was an uncommon card called roiling regrowth, but I can't remember the third reward. I tapped the collect button and my gold amount never changed but I still received the card reward.