I've been thinking of this ... It really looks more like some sort of anomaly caused by localized "stress" ... but, unless there is a wheel or some sort of spring pressing against the center of the film (pressure plate problem?) - I'd go with static electricity.
It doesn't take much to produce visible static electricity. If I allow my eyes to become fully acclimated to darkness, I can see a visible static electricity discharge when peeling the tape from 120 film, prior to loading the film on the developing tank reel. Faint, but visible. In all the developing I've done, I've never seen *ANY* degredation of the image from that discharge.

One thing you might try is **dilute** dishwashing liquid ... or, if you want to stay purely photographic, working stregth wetting agent - I use Edwal LFN, or Kodak PhotoFlo. Moisten a tissue and wipe it across the surfaces in contact with the film, and let it dry. That should provide enough lubrication to prevent electron stripping - static electricity.