White completely missing

I printed about two months with some Firebird white ink, one month before expiry date, so let's say it was not fresh from the shelf.. Caused troubles from day one, ink sticking to the prinhead plate, missing nozzles, etc.. Two days ago I decided to flush head with cleaning solution, and then with distilled water, since on white channel was constantly missing. Did well, after two head cleans, that one channel appeared, leading to three and a half channels solid. Next day print started perfect, for about 5 cm, then faded tremendously to the end of print. Did head clean, then again start fine, then nothing. Ink starvation, it seemed. I checked ink flow, ok, dumpers ok, changed them, nothing still, changed wims filter, air breather filter on white ink bottle, raised bottle, primed head with white ink, still no white ink firing.. Ink lines were changed two months ago, parallel with printhead and all dumpers, capping station to...
Printhead is not blocked, perfect waterfall from all 4 channels, there is ink on capping when cleaning, it fires white on spit ink pad also.
I'm in complete mystery, this is second time this happening in 8 months. Humidity is around 50-60%.
Somebody having any ideas?