My Phantom Vision App keeps going grey and freezing when I'm flying. I don't think it's a range thing as it does it when the craft is close (eg. 20m). If I land, cycle the craft's power, kill and re-start the app it comes back. Just killing the app and restarting (without power cycling the craft) doesn't fix it. Any ideas? (Phantom Vision II, running latest firmware - it did it on the previous firmware, am using iPhone 5).