The most likely cause is physical damage to the emulsion rather than a scanning issue, especially since another roll scanned the same way looks normal.

Based on the pattern, one possibility is tiny cracks in the gelatin emulsion caused by the film being rolled and unrolled, particularly in low-humidity conditions. If the emulsion was stressed, similar crescent-shaped marks could appear across many frames.

Another possible cause is static discharge from handling or advancing the film in very dry conditions, although static marks are often less uniform and more random in appearance.

A good next step is to inspect the negative closely, ideally with strong magnification or a microscope. If the marks are physical defects in the emulsion, you should be able to see texture or cracking on the film itself.