In some instances, firmware updates caused "Cartridge Locked" errors where the printer permanently refused to recognize cartridges that were installed before the update. Downgrading became a troubleshooting step for technicians attempting to unlock the hardware from this software-level bricking.
HP does not officially provide older firmware files. You must source the correct .rfu or .ful file for your specific model (typically version 1910A or older) from reputable third-party archives. Officejet Pro 8620 Downgrade firmware blocked by hp ? hp officejet pro 8620 firmware downgrade
This prevents the printer from auto-installing new firmware before you finish. In some instances