I have the exact same issue but a much longer story. We had a brand spanking new SC-S80600 delivered on 6th January. Within 3 days the cyan nozzle on head 1 stopped firing, almost completely. Phone call to local dealer and they came next day, diagnosed a faulty head and replaced head 1. This was after 3 days of use.
The engineer had barely left our factory 3 hours and the problem started again. Slowly but surely banding appeared in the print and within a few hours once again cyan had completely dropped from head 1.
Phone call to dealer once again and they told us to print with one head and they would have an engineer back ASAP. Engineer comes back 2 days later and replaces BOTH heads and printer works amazing. Engineer states he has never seen a brand new machine need 3 heads in its first ever week.
Fast forward a week until mid January and boom, same thing happens. Cyan completely drops from head 1. I'm straight on phone to Epson dealer and at this point pretty darn angry as I had just spent almost £20k on a machine that didn't work. The dealer blames the cold weather. Then he blamed our media. They basically blamed everything they could think off but we have two Mimakis and a Roland in the same room as the Epson and they all work perfectly well regardless of temperature or media and I expected the same from the Epson. I got quite irate on the phone and the dealer eventually gave in and delivered a brand new printer to our factory last Wednesday (10th February 2021). The director of the dealership, the salesman and 2 engineers arrive to install the machine and make sure everything is perfect. They install the machine and all seems fine. We print on it on Wednesday, all day Thursday and all day Friday and everything is great.
Then this morning (15th February) my print operator comes into my office to say printer is doing exact same thing. I go in to see test print and this time it is light cyan almost completely gone. See attached picture.
STRAIGHT on phone to dealer. Sent them photos. Lots of phone calls and eventually dealer offers a full refund. I tell them I don't want a refund and that I just want my printer to print in the way that it is supposed to. Dealer admits they have no clue what is happening and don't know how to fix it. I asked can Epson trace their quality checks back with the serial number to check in case its a dodgy batch of printers and was told Epson builds their printers with robots and therefore they do not make mistakes and quality is never an issue, no machines ever come back, nobody ever complains etc etc etc.
After numerous phone calls (and some angry words) the managing director is making the 4 hour trip up from Dublin tomorrow with an engineer to find out what the problem is. I have stated that I also want to know EXACTLY what the problem is. My print guy has been in the graphics game since 1984 and has probably forgotten more than I know (I'm in the game since 1999) so I'm pretty confident it's not user error although I have asked that the engineer check all settings on the machine itself to make sure everything is as it should be.
I will be following this thread and I will let you know how I get on tomorrow after the engineers look at my 2nd Epson SC-S80600 in a month and see if they can figure out what the heck is wrong with it!!