You draw a squiggly line down a length of film with a sharpie, and inch it through the camera to see if the film is held in place when the shutter is open, if you see that the film is not held stationary when the shutter is open, then the shutter and movement are out of sync. This would also cause a verticle streaking in the footage which doesnt seem to be the case in your framegrab, but who knows.
When I see the pressure plate reflections in my stills they usually have a slight horizontal streak in the center of the frame and usually have a burned right edge, made me think it could be similar.