GH4 picture goes darker on it's own
 

Had the GH4 go darker while filming the same scene. It just gets darker for some reason. Switched to iA and it was the same. Turned the camera off then back on and it was back to normal but got darker again in a few minutes. Had to quit using it. Used it for a outside wedding and ran for 1 1/2 straight {Indian Ceremony}
and it was fine. Next night at a indoor one it did it again, so I finished the night with FZ-2500.
Anyone ever have this happen??