Thanks for posting. This is the kind of abrasion I expect to see if a sharp corner of one sheet (or another kind of sharp/pointy protrusion) touches the emulsion side of another sheet when wet. What happens then is that the emulsion is locally scratched away, and the little peel clings on to one end of the scratch and forms a high-density mark there.
Scratches on dry film tend to manifest as high-density pressure marks mostly, or also low-density scratches where the emulsion is actually lifted, but you'd then also get a little high-density pressure mark at the start of the scratch where the pointy object starts to dig into the emulsion.
So my first thought is that this is caused during the wet stage of the film.
Edit: some examples for comparison.
This is on color film, but illustrates the principle I indicated above: emulsion is peeled off in places (the red & yellow stripes) and then deposits in a little curl/peel at the end of a scratch (top left in this image). The red/yellow anomalies are explained by the structure of color negative film; you get minus density/black on an inverted B&W positive.
This is abrasion damage occurred during careless respooling of B&W film; note the high-density anomaly (as a result of pressure 'exposure' of the emulsion in that place). There's also minus density abrasion, but generally not in a neat little peel that sticks to one end of a scratch and then survives processing there.
