Usually this is due to allowing the printer sit and the pigment falling from suspension. If the printer was sitting for a few weeks. Remove the carts, shake them, then run three power cleans to move freshly shaken ink into the system. Should be normal. But if this does not cure it, then possibly the inks in the carts are contaminated. If that is not it - are you sure you do not have an ink that dropped out? Did you run a nozzle test after a print to confirm. Not usually be anything else than one of these.