Game shuts down


The game shuts down randomly. It happened a few times during the stage fights. But this last one happened during challenge event. The advanced levels. I lost out on the loot and world energy. I cannot get a screen shot because on my Ipad the screen goes dark as if the whole device shut down. And I have to click out of the dark page. And it makes me open the game all over again lIke I was never playing it to prior to the issue occuring. Any help on this matter will be much appreciated. Thank you!