@ Don Promillo. Yes, I see your point about not buying the film. But for one thing I like it (when it works) and for another I'd like to know if it can be solved. Obviously switching is an option and I;ve just ordered to Portra 160 to try.
@railwayman3. I've contacted the lab. Still waiting for the manufacturer.
New observation. The second to last frame of my latest roll has a hard line horizontally across the middle, from the edges inwards, of the blue colouration. I've not seen or noticed this before. My gut feeling is that this mark is not consistent with light piping because it has a hard edge?