topsy1,
May I ask you what kind of videos did you use when you experienced this type of difference?
Was it a regular movie? If it is a regular movie, which theatre mode was it played in? Is it cinema, void or space station?
Or was it a 180/360 video?
Since we are doing complicated 3D scene rendering during the cinema and space station scenes, so the frame rate might be more influenced in these two theatre modes.
Andy