Lines on the negative

I developed my first film roll in C41 Cinestill Kit and got this type of lines on 4 or 5 negatives, everything was done according to the instruction. It's not a big deal, but I'd like to know what I did wrong in order to prevent such issues in future.

Hi Ivenhoe,

That is minor fogging (note the red streaking), caused by stray light reaching the film. You probably have a small light leak in your camera or (less likely) the film cassette, but the latter seems less likely because this is frame 23. It's probably a problem with the camera; check the camera back is fully light-proofed, the light seals are in good condition (they can decay with age) and that the back closes properly, especially along the bottom.

Good luck,
kevs.