And you will most likely discover that if any of those sections were in the image areas, that those areas are now clear.
They usually are a sign that parts of the film were pushed up against something solid - either more film or the reels themselves - and no chemical was able to get to them. That will most likely mean that those areas didn't get any development, before they didn't get fixed. So when you re-fix the film (after loosening it) you fix away any un-developed latent image there.
Sometimes that contact can happen sfter development, and before fixing, but that is rare.