I believe that 2880 printhead I sent you had a couple of nozzles that would trail up or down like yours is showing. However, the nozzles from the 2880 stayed like that and didn't straighten out after repeated head cleans priming cycles, flushes using the syringe, etc. From what you've said, yours clear after a few cleaning cycles.
Now, after I removed the head and immersed it directly in piezoflush, many solid chunks came out into the flush. I was unable to test the head again to see if my efforts had been successful, so I cannot say if that technique would clean up such a nozzle check. I almost wish I had another cheap or free 2880 to play with. I almost wish I had the time to play with it too.
My hypothesis regarding the printhead is that over time, if the head is not maintained, pigment will most certainly accumulate at various points between the cart and the nozzle. If such an accumulation were to break free inside the head, it could settle on the nozzle. Cleanings would stir things up and clear the nozzle check, but they would eventually settle out again and block the nozzles. I suppose that a fine chunk could get trapped in the nozzle and cause to misdirect the flow.
I'm not an expert here, of course. But I was surprised just how much crud came out from the printhead when I soaked it. This was after filling the carts with piezoflush and performing many head cleanings, treatment with the paper towel under the head, and flushing with the syringe. It would not surprise me that particles could be in suspension inside the cavities in the head.
This information probably doesn't help you, but...