How was the agitation done for each step (fixer, developer, etc.)?
Jim, on the largeformatphotography.info site there is a user, tuco, who is actively using a GX617. Suggest visiting the site and contacting him.
Can you see the defect when viewing the negative closely with a loupe?
Shutter. Typically happens at higher shutter speeds. The lighting in the examples suggests higher speeds, faster than 1/125, may have been used.
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