It came to me that perhaps the rotation was "too slow" and the developer flow was too smooth so as to cause a non-random flow around the sprocket holes. (one of those early morning, why am I not sleeping brainwaves)

Since I've not had any problems with 35mm films and other developers in the past while using Jobo at the 75rpm setting (yes, I calibrated the various settings when I purchased the used processor...) and only with Pyrocat HD and the slow (~28rpm) setting, I thought I'd try a roll at each setting. Will update tomorrow when last roll is dry and contacts made. (looking for agitation artifacts and increase in general fog / stain level)