Okay, and fogging is in the last three frames. I just looked up a quick video on loading the Super Rollex film backs, it works very much like my RB67 120 backs -- so those last frames would be by the in the gate (frame 10), and by the door latch (frames 9 and 8) after you expose the last one, before you wind on through. A bad light seal at the latch could cause fogging on those three frames only if it's small and you don't unload immediately after finishing the roll. Premature unlatching could do the same. If you had a leak at the hinge, it would be more prone to fog the first three frames before exposing the first.
Assuming you wind the film at least until the backing tail releases from the supply spool, by that time the actual film should be protected, but with the distance between spools on this type film back you'll want to wind on another two or three strokes of the lever after that to be sure the backing is all on the takeup spool. At that point, the leaf spring under the roll on the takeup side should be holding the backing in place, allowing you to open the back and hold the backing with your fingers while you unload, fold the tail tab, and seal the band.
If your unloading procedure differs significantly, that may be the source of your trouble.
If you're getting the paper tail wound all the way, then your fogging is most likely due to a bad light seal on the latch side -- and you should check the rebates on the rest of the roll for similar, if fainter fogging where the film stopped between frames.