It they were light leaks they wouldn't be that uniform.
Here's another similar case https://www.photo.net/forums/topic/184842-what-happened-to-this-film/
Look for jay_de_fehr answer.
Ah, I like it. The hypothesis is it is stress marks caused by rewinding the film backwards into to the cassette - causing it to go around a sharp corner. The thing to do now is to make an experiment that shows this effect. As I said above, the proof is experimental evidence that makes this happen on demand.
I'd volunteer but I used my last spool of 'trash' film (AKA really, really outdated antediluvian Arista (probably Ilford something or other (could be Dupont, explains the 'Buy War Bonds' admonition printed on the box)) that I used up by buying too many trash cameras (did I say C3, Solina, trashed Nikon...?) and feeling I need to shoot a test roll in each (P.S. the old Arista holds up remarkably well)).
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