Weird Pressure Issue...?

Hi guys, se we have a weird one. I’m having very scattered nozzle patterns very sporadically on our 4900. We recently DIY installed a “new” print head from a printer that was literally printing out NO nozzles having not been printed on for some months. I piezo-flushed the head very gently with a syringe, and it came back immaculate after a CL3 cleaning. It worked for a few weeks without issue, then it started dropping many of the channels almost entirely. I JUST replaced the capping station at the same time as the head, and the selector unit was replaced about 2 months ago.

Some days it’s fine, others it’s very spotty. Today we started with a perfect nozzle check, then it started banding after a few prints, and sure enough, about half the channels were severly spotty. Is this a pressure issue? Do I really need to replace the selector unit again so soon?? Could this be an issue with the head itself?

See nozzle patterns in chronological order attached below.

Any advice appreciated~!
Thank you!