Where light leaks show depends on where and when the leak occurs/occured.
The 'usual' light leak is caused by the dark slide slot seal not sealing anymore, and light entering will hit the image area of the film. The black borders are that, black i.e. unexposed, because they are shielded against light by the edges of the film gate, and light cannot get there through a leaky seal.
Leaks occur at other places in Hasselblad backs too, but only very, very rarely.
One other place that could be responsible for the pattern we see is opposite the dark slide slot, where the magazine's front plate rests on the frame of the shell.
If the plate doesn't sit properly (perhaps because the screws aren't done up tight, or because it wasn't put back properly the last time a dark slide slot seal was changed) some light could get in through the slot through which the gears of back and camera engage. Could, but very unlikely.
It would be consistent with where the lighter band is.
However, it would not be consistent at all with how the lighter band stops where the lighter part of the subject stops also.
Other places where light could get in exist too (for instance, if the magazine sits rather loose, light could get in between canera and magazine), but again it would be very hard (impossible) to explain how light entering from anywhere where it shouldn't could correspond so perfectly with th elight entering through the lens during exposure.
So despite the many words above, i think it is not a light leak.
The thing to figure out is how this artefact could echo the image content, appearing where the image itself is a bit lighter, not where the image is dark also.
The fact that the dark edge of the frame, with the Hasselblad "V"s, remains clear could either indicate that the thing occured either when the film was exposed (light entering through the lens bouncing/reflecting off something. But what? And how?), or when the film was developed (edge between clear part of the film, i.e. where there is no silver to be developed, and exposed, developable part of the film. So an edge-effect of some sort?).
The fact that this only appears in one film would point towards it being a processing issue.
But it's not 100% proof that it is.