I processed three 120 rolls of film and one 135-36 roll of film, all Tri-X, using the plastic Jobo reels. Two of the 120 rolls have the black edges sporadically but not intruding into the image frame. The other two rolls do not have any problem. The tank was checked for level before and reels had been cleaned with a tooth brush. For some reason the 120 emulsion must be pressed against the plastic while the developer is in the tank and later the stop bath and hypo get to the edges. I always remove the film from the tanks and use a plastic bowl to PhotoFlo. Based on other threads, I believe that I have taken all the precautions that I can and this is just the way it is.