I have switched tanks and tried one Jobo and one Paterson, no difference there. I think the problem gets worse on the last frames. But to really see that I have to shoot at least the first, middle and last shot under similiar conditions and the same subject/background. But that might be the way to go, I really don't like when I'm not understanding why things get F*d up.
Btw: the first 5 rolls I have tried all come from the same pack. I have no opened another pack but they are bought at the same time so probably from the same batch. Maybe I get another brand to try just to eliminate film error.