We have seen a strange issue with one of our machines, not an Agfa. A head test looks good when a nozzle test is printed, but we follow that up with a density test, which is essentially one head getting all of its nozzles in a singe swath along the width of the material or printer. The head would start out fine but as it went on nozzles would drop out. The first check would be to make sure the ink flow is good. Sometimes a head can be starved for ink maybe the pump not pumping ink fast enough to replenish it. Or if there is contaminates in the ink line themselves and possibly filters. The head is the generally the last place they want to look as it is, most of the time the costliest to replace. I hope this gets resolved for you, I know how FRUSTRATING this can be. FWIW most printer manufactures will cover print heads for the first year as long as it is determined that a head strike is not causing the issue.