One of our guys was on site today installing a new HP M425 for a client. He unpacked the printer and everything worked great except for the scanning. All scanning was 100% black.
He rechecked the whole unit and there was no packing material blocking the scanner. Nothing left to do but call HP support.
HP support had him flash the firmware to the latest version and scanning began to work fine. Very very weird. I would never have guessed in a million years.