Crashes after awhile

This is an amazing art tool but I am on my phone and I am plugging away adding things and all of the sudden the screen disappears and I have completely lost what I was working on:(. It's very frustrating if I don't save my image after every change because it will disappear if I don't save all my image changes. If I save it is ok. Because it will crash and I will just load up my last image:). It is very frustrating:(