What happened?

Do you do a pre-rinse or was the spiral wet from the last roll of film?

Since the print is lighter in the problems areas the negative should be darker in those respective areas. Can you see anything when looking at the negative on a good light box? If so I would suggest a stain or hard water buildup of some form. Touching layers on a reel, water spots ahead of development, etc. always result in a 'thinner" negative in such a problem area.

Did you put the film in the tank for a while before souping it? If some moisture was in the tank, it could have affected the film prior to developing. I got some weird results on a roll of negs when I put the film in the spiral, dropped it in the tank, and then never ran the soup through the tank for about a week.