Right, negatives are clear in those areas. So that rules out a light problem, it seems like just somehow there wasn't any development along the film edges of six frames, even though the film edge markings look fine. I'm trying to figure out if it could be something in camera but I've developed film from the same camera/lens that was taken after those pictures with no problems.
I did re-fix the film tonight so if nothing else I've learned all about not fixing film correctly. The negatives look much better and hopefully that will explain some of the problems I've been having with scanning.