Chromebook Having Crouton troubles

So my sisters chromebook has crouton installed to make productivity much simpler. It was working quite well for the past months but suddenly an issue has reared its ugly head. This being that when she is using ubuntu the screen jumps back and forth from ubuntu to chrome and back again, similar to a screen saver. I think that it might be something to do with the sleep function of ubuntu, however this never has happened before.
Any help is greatly appreciated.