Colosseum issue

A few days ago when I wanted to do my daily battles in colosseum like everybody else, I simply put the battle on auto and I left. After 5 minutes I got back and my game was frozen, i tried to press the buttons or to put pause and resume playing but it didn't work. My only choice was to forfeit the battle and start another one. I don't know why this happened and I encountered it a few times.