I copied 4 permanents with Dopplegang, Resplendent Angel, Fiendish Panda, Case of the Uneaten Feast and Felidar Retreat. The lifegain from Case and the resulting +1/+1 counters for the Panda caused what seemed like hundreds of effects to go to the stack on my side. I checked resolve all and sat there while the game engine did it's thing. At a certain point I got a warning that I needed to take a different action or the game would result in a draw, which is what ultimately happened. This seems unfair and is punishing for the player who casts Doppelgang. If there were too many triggers or it took too much time, the game engine should just short-circuit and resolve all of them or ask the opponent if they would like to concede or proceed with the game.