Puggo - Jar Jar's Yoda said:

... could be a damaged sprocket hole.

I only noticed one of these when playing the clips (over & over), but hadn't considered the mechanical aspect of it. That's good, as it would mean the frames are all there and such a misaligned frame could be easily reconstructed.

Have you noticed the rhythmic, slight, bright/dim variation in your other captures like I observed here? It can be seen on any steady background that stays on screen long enough to pick up on it. (That's why my earlier sample-frame color correction was not stable across even individual shots.)