Can you show us a picture of your nozzle check (Test Print) to help verify that there's no other issue going on?
Have you experienced a head strike or replaced a head recently? Do you have OEM heads in the printer with the correct head ranks input?
I am not sure what DT1 vs DT3 means, but if I had to guess, it is dot size. If this is the case, you're only experiencing that anomaly when the printer attempts to send the larger dots. That should tell us something.
Player is probably correct. You may be looking at a new cyan head, new head cables, new carriage cables, or new main board (or maybe even just a fuse--though I believe the entire channel would drop out if that was the case).