I just processed another roll from that camera and same problem. Instead of being 3-4 frames at the end of the roll this time it was 5-6 frames in the middle of the roll. It was a bone dry reel and everything seemed fine loading it and when it was coming out of the tank. I really don't think there is a problem with the processing, I've done enough rolls to know when I've screwed something up.
Since the sides of the negatives are dark this is leading me to believe it is a camera issue and the film is not getting light somehow. Would it be possible that I have film problem? Maybe the film is curling and so the top and bottom edges are not getting exposed? I was shooting at -30 C and the camera was very cold so I am wondering if this is causing some kind of problem in the camera.
I'm going to try shooting a test roll indoors to see if cold is a factor, and also will try a different film back to see if that is part of the problem. Maybe my pressure plate isn't working in the cold?
Here are some more scans, as always any thoughts and feedback welcome.