I had the same issue with the HP Officejet Pro 8600 Plus(circa release 2012). It had a defective printhead. Replaced by HP. (There was a recall). HP later re-badged the name, and I have the newer Officejet 8620 Pro. It has the 8.5x14 scan bed, which is no longer available by HP. The legal scanner was useful 10% of the time.
BTW<> my HP 8620 has 14200+ pages printed. Install date of printer is 08/2016.
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HP Envy 8 5010 Tablet (2) HP DV7t i7 3160QM 2.3Ghz 8GB Printer -- HP OfficeJet Pro 8620 Legal Custom Asus Z97D, I7-4790k, 16GB RAM, WIN10 Pro 64bit, ZOTAC GTX1080 AMP Extreme 3 fan 8GB RAM, 500GB SSD, Asus PB287 4k monitor, Rosewill Blackhawk case and 750W OCZ PSU.