I have not used an acid stop bath in at least 25 years and have never experienced the problem you describe. However, I do know one of the causes of this problem.
If you put the reels in PHoto FLo youwill get the increased density along the edge because Photo FLo acts as a catalyst to the developer.
In order to remove traces of Photo Flo from the reels it is necessaryto scrub them in hot water with a toothbrush.
I can't believe this! I just measured my rodinal in the same beaker that I measured my photo flo in! It looked really BAD and so I thought it was from the marbles. Then I realized what I did. So is my whole roll kaput? Is it going to be dead in the developer? I remembered about this thread and the problems with photoflo. I was planning on a 1 hour stand development. I suppose it's too late to save it? :o Boy do I feel stupid!