PH Status plot defective - despite new printhead or switching PHs

We have the following problem: The print head status plot does not show a large number of defective nozzles on Pen 3, but rather poorly placed drops in large areas (blurry/misaligned). We have installed a new original PH when this occured. Now if we swap the Pen3 and Pen4 print heads, the problem does NOT shift, but remains with Pen3. Printer does not throw any errors, despite regular low ink or calibration stuff. We have tried the following without being able to solve the problem: Multiple intensive cleaning of the print heads. Manual cleaning of the print heads with distilled water. Cleaning the PH contact strip in the carriage (according to the HP manual). Checking the primer rubbers for integrity and correct fit. We could not find any other possible remedies in the manuals.