I used to print quite frequently on scraps and off-cuts of canvas, on a 9800. They tended to curl up and cause head-strikes on the edges of the canvas. I got plenty of ink splots and splashes because of this, and this would sometimes continue for a few prints after the scrap-print. So I stopped using scraps. Your image is reminiscent of the splots I got.
Not too surprising that it's Cyan only: if a biggish chunk of dust gets stuck to the head, and head cleaning can't shift it, then it's going to have a localized effect, isn't it?
I also got similar trouble when the printer was in need of a general clean and service. I'd been using it for almost 2 years on a mix of matte, gloss and canvas so the inside of machine was full of dust and muck (mostly paper dust that flies around when the cutter is in operation). I started getting lots of head clogs. Techs came in and cleaned up and it started printing beautifully again.
One thing I never got around to arranging was a dust cover for the machine. If I work with another large format printer again this will be a necessity for me.