I think that in general there are three plausible possibilities:
- Closure problem with a focal plane shutter;
- Scan problem;
- Development problem, probably restlessness;
- Light comes out in the camera or on the edges of the reel, or the reel is stored in a place that is very bright.
From what you said (1) and (2) can be ruled out: the camera has a leaf shutter, and the lines are on the negative.
I do not think it's (4) because the lines are too close to each other: If I had problems with the light at 120 (due to the exposed roll that sees strong sunlight), it was clear that light is coming in the ends of the light Roll and also through the backing paper in a wide band. I do not think that's it.
So I think it has to be (3): excitement or another processing problem. And while you process it yourself and paint is fussy about agitation, as it's designed for continuous agitation, I think that's very plausible. The bad answer is, "Buy a Jobo," even though they are terribly expensive (and the one I had was not electrically safe).