Here I am documenting my plight of installing and configuring an HP LaserJet MFP M28 M31 (all-in-one) printer / scanner  with Linuxmint 19.1 using the current HPLIP 3.19.3 drivers from HP.

Printing seemed to work straight away.  Scanning on the other hand took me a bit to figure out.

HPLIP system tray does not exist error on boot
Use Preferences -> Startup Applications and add delay


The dirty list of references:
  * HP Download - [[https://developers.hp.com/hp-linux-imaging-and-printing/gethplip|here]]
  * HP Instructions for installing HPLIP - [[https://developers.hp.com/hp-linux-imaging-and-printing/install/install/index|here]]
  * Fix for Allows the hp-plugin script to complete - [[https://bugs.launchpad.net/hplip/+bug/1813768/comments/5|here]]
  * Additional suggestions on things to try - [[https://ubuntuforums.org/showthread.php?t=2387244&p=13748997#post13748997|here]]