Sheet film.
Is it possible that the sheet was double exposed?
(I was out shooting a couple of days ago, and after making an exposure, I pulled out my notebook to make some notes, and realized that I had already exposed that sheet of film. Apparently put the darkslide in the wrong way.)
Did you, perhaps, have the emulsion facing the drum surface? Looks like the developer was blocked in at least two areas...
Also could be oil contamination on the surface of the sheet of film itself; maybe it was the leading or trailing edge of that particular slit on the web...
Looks like the film was loaded emution side in, and the developer could not flow thru the two sections of where it was touching the inside of the tube, and it made those channels thru the area. The black area would be clear on the negative, meaning it was undeveloped.