I saw this today & have no explanation for it, wondering if anyone here can help. I was in a share darkroom processing some film & also chatting with a woman who doing her film. I processed a roll in Rodinal, used water stop, the supplied fix & hypo clear then washed & dried. Film was perfect. She did 3 rolls of 35mm FP4 in Tmax dev, stopped in the supplied stop bath & then used the supplied fix & hypo clear. So very close to what I did at the same time. When her film dried I noticed that all the rolls had a weird brown stain on them as if they'd been soaked in coffee. Even stranger the stain wasn't consistent over the film. Each roll was about 80% stained but had patches that were clear film base. These clear patches were random shapes & randomly distributed along the roll. The film had been on plastic spirals in a Paterson tank but the film had been loaded correctly. I had idly observed her as she processed & it looked like she did everything correctly. I suggested she re-fix a strip to see if that cleared it but I had to leave so couldn't stick around to see what happened. Based on the above description, has anyone seen this before & know what causes it?