If you can wipe it off, or clean it off with film cleaner, then it might be the photoflood. However, this doesn't look like that.
It looks like one of two things. Either you are not presoaking, and are pouring the developer in too slowly. (One should also smack the reel on the table, or a piece of 2x4 once all the liquid is in to remove bubbles from the solution, before agitating.)
The other possibility, and the one that seems the most likely to me is that the film was crinkled on the reel. It was not touching, but dimpled a bit, making the flow of developer more active in that area every time it was agitated. Loading reels for med format is a delicate operation, and there are plenty of failures unless one does it often... Having done this thousands of times, altho' not much lately, if I did it today I would be extra careful to make sure no dimpling would occur.
Lenny