Thank you all for taking the time to consider my problem and reply. Unfortunately I have not made the slightest progress and just keep wasting hundreds of euros worth of film to the trash…
What I have learned so for :
1. It’s not a drying issue as I have hanged the film to dry horizontally. I have also tried with/without wetting agent. Although I must say that the streaks seem to follow the path of liquid runing along the film, it's unrelated. Also when inside the tank the streaks are parallel to the ground.
2. It’s not a light leak as I have tried 3 different cameras of different brand and all can show the same problem on some frames at least. Also used 3 different tanks at least and metal as well as plastic reels.
2,5. The streaks are mostly apparent on zones V-VIII, can be perceived in zones III-IV, can't be seen in zones I-II.
3. I contacted Ilford and they have been very reactive but say that to their knowledge it is not an issue that could be consistent with film defect.
4. I have tried different agitation method and although I think this might be where at least part of the problem lies, no change in agitation pattern, frequency and intensity changes anything except using a tank with one empty reel to generate more agitation. But I had mixed result with this method. I tried a 3 reels Paterson tank with 2 films only, 1 film (trix) was fine the other one (HP5) had slight streaks but much weaker as one the images provided as an exemple.
5. Ilford films seem much more affect by this than an old batch of trix I still have. Actually I can barely see it on trix and when I do I am unsure it's the same thing. I only recently started to use HP5 so is there something to dig here. I am not inclined in thinking that ilford films are faulty yet but maybe they are less forgiving with this particular issue.
So I am left to wonder the following :
1. does anyone know for a fact if a developer can do this ? Maybe I have a bad batch of HC110. I used this developer for decades without issues and now can’t get a film developed without those streaks… After all kodak had some serious issues with D76 recently.
2. Can a film defect (coating or other) produce this ?
3. Can a bad fixer be responsible ?
4. Can my tap water cause this ?
At this point switching the chemistry is the only thing I can see that remains to be tried. After that I guess I can't use film anymore, after 25 years of pratice it's crazy...