Seems like a memory or processing issue. I’m on an iPad Mini 2, 32gb, iOS v12.4. Crashes at least 5 times every time I attempt to play. Like a previous poster, it occurs when opening multiple chests, it occurs occasionally while in a battle, and when attempting to upgrade my collections. It’s probably because I’m on an older iPad, but it is frustrating nonetheless. I enjoy the game, but I think it probably uses way too many resources than my device can handle.