Any updates? I am having almost the exact same issue on my l26500, Onyx 18 is my rip. I'm using a brand new roll of matte vinyl (don't know how long it was in the warehouse) and am about 1/2 through the roll with the problems persisting. This is actually my second roll this is happening on.
Some colors are super grainy, some look like the ink is beading up, have the same "plasticizer" vertical waves in some places. Some spots look fine. Print head alignment and print head health tests look fine, color calibration prints look nearly flawless but then I send a test print and it looks terrible. I'm also having an issue on some solid colors where it almost looks like the ink is "starving" and I'll get splotchy areas where there is almost no ink at all.
I've cleaned the printer, recalibrated in Onyx, changed the substrate advance, switched the profiles, rebuilt profiles, tried adjusting nearly every setting on rip and printer even the service menu tests, all to no avail. I don't completely understand color profiles, but I've tried several canned ones and tried building my own, I've changed heat and vacuum settings, I don't know what to do with the ink limits and linearizations, but trial and error has not improved anything.
If I do 2-3 print head cleanings, print 18-20 pass, color variation correction on, vertical correction on, extra print head cleaning on I *might* get a passable print. At first I thought it might be from not using the printer for a few days, but I have used it a ton in the last week or two and it seems to only get worse.
Any other ideas? Is it for sure the media/plasticizer migration? I've been using the same brand media for about a year and just now getting issues. Also doesn't explain why my color calibration tests don't have this problem, which makes me think it's a profile issue, but I hadn't changed the profile when this started. I've been testing literally all day, any recommendations would be greatly appreciated.