My R2880 sits with cleaning carts at the moment, waiting for the time when I need to print in colour and have the time to do another clean and try again. My assumption is that once you've had cross-channel bleeding like this then at the very least you're going to need to clean under the head (again).
If you read that R2880 thread of mine then you will have read that I also had virtually identical issues with my piezo R1900. Widespread gaps and cross-channel bleeds. I hesitate to say this, but I think I have that one licked. I'm fairly sure that it was a faulty (previously unused) MK cart, as a clean, a refill and a fresh MK cart seems to have worked. Fingers crossed.
Given that, I am inclined to suspect that my R2880 problem is either more faulty carts from new (I've had two definites recently) or a fussy printer combined with less than prefect filling technique. So I will try the same carts again, taking extra care in the technique. If the problem persists then I'm going to replace the carts that seem to be leaking. If that doesn't work then I'll just buy OEM and put it down to experience. No, I may try one more thing before that, which is to buy some carts from the HK-based supplier that I used to get them from previously. But I've been through a lot of ink and carts (AND FLUSH!) so far and don't have a lot of prints to show for it.
Dan - I'm having a little trouble seeing your nozzle check scan clearly. Is it the case that your first two checks are ok? There's no cross-channel bleed in the first two? I think that's the case, but it's hard to be sure at this resolution.
Assuming so, and based on my experience so far, my view is that you've got a leak from the PK cart, and that's because either the PK cart is faulty, or you've not followed correct filling technique. You really do have to fill but not over-fill the carts, tap them gently, let them sit for a while, put them in the printer and let them just sit there for 15-30 minutes with the head still in the ink exchange position. Only press the ink exchange button once they've sat there for the requisite time or longer.
If you really have done all this and all the cleaning, my suggestion is to clean again, replace the PK cart with a fresh one, and try that.
Let's see what Dana suggests. There's always the humidity issue, but unless you're in the tropics I still find it hard to see that leaking is caused by humidity, and the evidence to date is that that wasn't the issue with my piezo R1900.
p.s. It's interesting that you're getting issues with the same cart (PK )as me. I really think that there's a chance of a bad batch out there. Alandb hasn't provided enough info in his thread, but I have a hunch ...
p.p.s. If your carts with ink have been in use for two years, rather than just purchased two years ago, then they may need replacing. They don't last forever in my experience.