Apple TV 4k and Quick Start not working all the time

[PCFan]

I noticed that even when I have Quick Start enabled in my Apple TV 4k's settings, some movies and most TV episodes I have in my iTunes account seem to be ignoring the Quick Start feature. I witness this by bringing up the progress bar and if Quick Start is working then I will see a solid white progress bar but if it's being ignored then I will see the progress bar gradually fill up to then end. Also in Good Fellas (remastered edition), enabling Quick Start gets rid of the compression artifacts in the beginning of the movie where it shows the car traveling at night to the woods. With Quick Start disabled, there were compression artifacts in those scenes. Does disabling Quick Start result in a lower streaming bit rate or is this a glitch with Good Fellas (remastered edition)?