Is my Panasonic 14- 140mm lens faulty?
It might be a problem, if there was no camera shake when that happened. Are the pictures you are showing the complete frame of the video and not a crop?
I have the same combo and have not seen the frame moves in the direction like what you are showing. Occasionally, the lens re-focuses as the sensor locks on items in the back or foreground, but that would cause the image to blur a bit and resharpens, not moved in the up/down or left/right direction. The pictures you are showing looks like it was caused by a camera shake.
To test this, I suggest to mount the system on a sturdy tripod or mount on a stable ground and let the camera record with and without IS.
Edit: Also, are you operating the zoom ring when this happen?