Can't connect to HP Scanner

On both Ubuntu MATE 18.04 and Slackware 14.2 I can print to my networked HP LaserJet Pro MFP M148dw. I set it up on Ubuntu using System > Administration > Printers. I told it to Add, and specified a Network Printer. It found the printer, and I can print to it from LibreOffice Writer. (I expect it will print from other things, too, but haven't seen a need to try.) I set it up on Slackware XFCE using Applications > Settings > Print Settings. I clicked on the plus, gave my root password, clicked on Network Printer, told it to find, and it found it. I can print from Slackware.

If I try to use one of the tools under the hp icon on the top line of the screen, nothing appears to happen. When I run hp-devicesettings from a terminal I get:

dick@ENU-1:~$ hp-devicesettings

HP Linux Imaging and Printing System (ver. 3.17.10)
Device Setup Utility ver. 0.1

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

error: No device found that support this feature.
dick@ENU-1:~$

If I run (Ubuntu) System > Preferences > Other > HPLIP Toolbox It opens with an warning window (yellow triangle with an exclamation mark in the middle) that says, "No Installed HP Devices Found. And then gives instructions on setting up. It recommends running hp-setup in a terminal. When I do that and click on the radio button for Network/Ethernet/Wireless network and click Next, I get an error window that says, "HPLIP cannot detect printers in your network." The terminal has the following:

dick@ENU-1:~$ sudo hp-setup

HP Linux Imaging and Printing System (ver. 3.17.10)
Printer/Fax Setup Utility ver. 9.0

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
Searching... (bus=net, timeout=5, ttl=4, search=(None) desc=0, method=slp)
error: No devices found on bus: net
error: HPLIP cannot detect printers in your network. This may be due to existing firewall settings blocking the required ports.
                When you are in a trusted network environment, you may open the ports for network services like mdns and slp in the firewall. For detailed steps follow the link.
                 http://hplipopensource.com/node/374

Done.
dick@ENU-1:~$

If I try to run the HP software on my virtual Win7 machine, it won't find the printer, even when I give it the IP address that shows in the printer's status window.

It appears that something is keeping the HP software from seeing the printer. I'm guessing it's the same thing keeping xsane from seeing the scanner. When I run xsane I get "no devices available".

Did setting the printer up using Ubuntu or Slackware tools instead of HPLIP cause a problem? Or is there something else I'm missing?