I know what you mean. Brightness is pulsing in those scenes..from a little brighter to a little darker. I noticed that on one Picard close-up, but don't remember the episode.
Just a very few seconds, and once the angle changed to another actor and then back to Picard, it has vanished.
That's precisely it.
It is possible it was caused by not letting the film scanner "warm up" for 10 minutes.
Though as expensive as they are should not really need that.
If the drive motor was just an nth slow or fast feeding the film, that can happen. I've had
that happen with a telecine projector motor that had worn bearings.