Is the 360 not like the 26500 – by that I mean head config of 2x K+Y, M+LM, C+LC
Mike.. you’ll need to go into the menu and run some test plots. sometimes head cleans will sort it out, other times you’ll need to replace the head. typically I replace all the heads in the course of a 12 month period – usually only ever due to quality rather than the head throwing a terminal fault. That said, if you’r machine is under warranty, I’m pretty sure you need to swap out “out of warranty heads”, details can be found under “printhead information”
it could be something as simple as that. I try to always carry a full set of spare heads. changed in a couple of minutes and gets you back up and running. I think HP heads around £80-£100. do a print test to see which has gone.