I vote for a light leak in the camera.
If it were a development problem there would be a dramatic increase in contrast and not much fogging of the shadow areas of the image.
The light leak isn't in the processing stage as the clear rebate areas of the negative show no fogging, indicating the fogging happened when the film was inserted into the holder.
If the problem happens in the same area on horizontal shots (i.e. it rotates with the film) then the problem is in the rotating part of the camera's back.
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