I was playing Dalaran Heist and had a Shifting Scroll spell in my hand that turned into a “Duplicate” mage secret, which I put into play. I ended my turn and the enemy killed my Pyros, which returned to my hand as a 6/6 and the Duplicate secret activated. Two 2/2 Pyroses were copied to my hand but instead of the “Duplicate” card popping up, the game showed me the Shifting Scroll and it got stuck there. My only option was to quit the game.
I have screenshots of the event if needed.