Thank you for your help! Sorry for the late reply!
I do not use anything but water to clean the equipment. Just rinse it thoroughly with running water. I bought a second-hand JOBO machine together with some bottles and, indeed, I used two of the old bottles to store the chemicals. They looked clean though (and I rinsed them well).
Anyway, now I mixed a new batch of chemicals, poured them into brand new bottles, and went through all developing steps carefully with no mistakes. (not that I'm aware of any)
The result is this:
I boosted the contrast on the images to better see the streaks.
As you can see, they are much less but still visible. Plus now, there are also some leaks in the corners of the last three pictures.
Also, the two last frames are totally damaged in a different way:
When I opened the tank and took out the reel, the last piece of neg was touching the negative inside, a little bit. But only the very last two frames are affected (not the other part of the negative that was in touch), and it looks more like a light leak. (In the last picture behind the chick is a blue sheet, it's not a blue streak).
I load the exposed negative on the reel using a film changing darkroom bag, in daylight (not darkroom). It is not precisely in the sun, inside a room, but maybe some light leaked inside the bag?
Next step, I will develop an older roll of exposed neg, that I store in the fridge. Different package, different times of exposing the film. Also, I will load it on the reel at night, using the bag but in darkness.
Let's see the results.