If possible, try to see in the Gui (compass sensor monitor) what happens when all MultiCopter motors are running around 70%. off course without Props (-: It's possible that these motors give some noise to your sensor/8-bit board.
Otherwise check your power as Garug says or try to power your gimbal with a other battery.
Sounds like my problem. Will report after the testflight today with minor changes (Power setting / position of frame IMU). What kind of camera are you using?