I found that my Paper Thickness (head height) was set to Low by default. I changed it to Standard and have not seen the problem since. I imagine you've already checked that setting, but sharing this just in case...
I have a pretty new ImagePROGRAF PRO-300 (purchased last September, but not used much until lately), and it has the same or similar problem. I did some small (4x6) prints today on Red River Palo Duro Baryta paper, and each has one area, roughly the ...
