A few weeks ago I sent out two rolls of Scala and a roll each of Velvia 50 and XP2 Super to the lab and in some of the frames on the processed negatives that came back, there were light patches (please refer to the attached scan). Only the Scala & XP2 rolls had the problem, and in most of the frames in each roll (120 size). All the shots in the Velvia roll came out fine. And as I mentioned, some of the shots in the affected rolls also came out fine. I initially thought that the lab (Duggal in NYC) had messed up, but after thinking about it I am not so sure. Coincidentally, the Scala & XP2 rolls were shot in the same SQ 120 back on a Bronica SQ-A. I purchased this from KEH. The Velvia was shot in a SQ-i back which came with the camera.
My question is: do you think this is a light leak problem with the specific back in question or is it a processing issue? If it is a light leak on the back, why were all the shots not ruined?
Please note that I have only one body and was switching the backs when I wanted to shoot the Velvia.
PS: My apologies for the poor scan quality - my scanning skills are non-existent.