I have had the black screen at times. I close out the app and reopen it and everything works fine. Your situation appears to be more complicated though.
Ok. I guess I'm out on this one. Thought maybe the gimbal may be actually moving but you couldn't see it because of the pixelated screen which is common in some Samsung devices.
Have you checked if your gimbal is moving when you can visually see it while controlling it? What device are you using to control your mavic pro. Not a Samsung device is it?