After upgrading from 3.15.9, I could not use my HP Photosmart B010a integrated scanner. After lots of fiddling, I found that there was no changes in udev rules or configuration that could justify such problem. sane-find-scanner would correctly identify the USB device as a scanner but scanimage -L would not list it. After downgrading to 3.15.9, it instantly started working again.
Any chance this Lauchpad bug is the same issue you are experiencing? https://bugs.launchpad.net/hplip/+bug/1521687 If yes try enabling the snmp USE flag as a workaround.
indeed, enabling USE=snmp does make the scanner work again with 3.15.11.
This should be fixed with net-print/hplip-3.16.2 which is now in git.