Probably your network printer was not set up with the "hp" CUPS backend but with "dnssd" or "socket". Scanning only works if the print queue for the device is set up with the "hp" backend ("hp:..." URI).
Probably your network printer was not set up with the "hp" CUPS backend but with "dnssd" or "socket". Scanning only works if the print queue for the device is set up with the "hp" backend ("hp:..." URI).