It's usually when I press the sleep button in the quick camera mode. It just turns off, sort of bricks, doesn't do anything. I hold the sleep button to turn it on, doesn't turn on. None if the buttons function. Then randomly the lock screen appears without the apple logo when turning on and everything's functioning again. Happens to my dads iphone too, except he doesn't need to touch any buttons, it happens by itself. Has this happened to you.