Invalid MAC od device reported by Nighthawk X6S R8000P

I have a similar problem (V1.4.4.94_1.3.56 firmware, Windows 10).  Was previously able to assign IP to 2 devices, HP printer and home stereo (constant connection issues, after assigning IP, issues resolved).  Added new printer and constantly could not find unless I updated IP via HP Print and Scan Doctor program.  Noticed that if I did not update via HP Print and Scan Doctor, the printer did not show up on router's device list, shows up after running Scan Doc.  Tried assigning (or adding) printer to static IP, but invalid MAC address error popped up.  I tried assigning static IP to other devices, same invalid MAC address error.