This week I replaced one of my white print heads after trying everything else, that line would not pull white ink in and when I swapped with a good one everything worked fine. As soon as we replaced that print head, the other one started to feel left out I think.
Current situation is the "bad line" will load white, clean, print great nozzle checks, print 1-2 shirts perfectly, then while sitting idle for a couple minutes the ink seems to go back to the cartridge/drain back out. Like it can't hold the suction/vacuum of the line. I've checked connections. The cap drains properly. Have replaced filter on the line. We can keep using it if we either reload white ink, or do a tube flush and a cleaning, starts right back up.