I noticed the second set of scans were both HP5. If this effect was confined to HP5 rolls then I think the finger points back at Ilford. If it is on HP5 and FP4 rolls then it is something that was common to the treatment of both rolls.
The extreme consistency of the horizontal pattern is very puzzling, though there is some slight variation in spacing - which would indicate that it wasn't due to something scraping across the film but that some intermediate substrate was involved in transferring the pattern to the film. Say if adhesive is put down on tape by a set of nozzles and then the tape is applied to the film - even though it seems through protestations that tape is being ruled out.
Whatever happened - it wasn't supposed to happen. Obviously something went wrong somewhere, so claims of 'we never do that' have to be taken with a grain of salt - somebody or something did do something that shouldn't have been done.
Which leads me back to sticky tape getting where it shouldn't and then being pulled off with an 'oh, damn' without realizing the triboluminescence would image on the film.
Murphy's law trumps all others.