ink starvation is a cause of either insufficient vacuum below the print head or insufficient ink supply above the print head.
first thing you do is determine what color is dropping out. swap ink lines with that color location with a different adjacent print head. you will be running the wrong color to a head. make up a graphic that is a big square of the color you are losing and the color you are switching (big cyan rectangle, big yellow rectangle or whatever).
does the ink starvation show up at the new position of the damper/line swap? or does it remain at the previously starved ink? if it moves to the new print head, you have a supply issue. let's say cyan is dropping out. you move cyan to a new head. cyan still drops out. ink supply. or cyan now doesn't drop out, but yellow drops out. vacuum issue.
do that first and then get back.
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supply side is caused by clogged dampers, clogged line, uneven printer, high ink viscosity, clogged cartridge needle, faulty cartridge.
vacuum side is misaligned capping station, clogged pump tube, faulty pump, dirty cap or worn cap, clogged print head.
if neither of these can be isolated. than you can do a data cable swap to see if it's an intermittent data issue. but i doubt it. data issues are usually the result of printing gibberish. not lack thereof.