When the video camera is recording, the image shifts gentley back and forth on the screen and the resulting video has the same wavey issue.
shooting 4k 30fps.   I noticed that the problem was worse when flying and about half speed and would stop once the aircraft was brought to a stop.
It doesnt do it on every flight, but did do it with two different batteries.   I have upgraded all components to the latest version.   
Anyone have a solution?

Try to do the IMU and gimbal calibration.  What camera are you using?  X5 or X3

You are getting that jello effect. Go over to you tube and there is a forum member named Jim Hare who is a pilot with super video skills with  his  aircraft.   This effect is quite often eliminated with filter on the lens of the camera, this way you can lower the shutter speed and eliminate the wavy ( Jello effect) video.

give it a go with filters and watch Jim's Video's

cheers- donnie