Linux Mint 64bit 18.0, HP Officejet-Pro-6970
I get no devices available when I run Xsane when I do $ sudo xsane
I can print wirelessly to the printer scanner, but not scan. I can scan from from the HP to USB.
Scanner was working previously.

I did get a notice:
HPLIP cannot detect devices in your network. This may be due to existing firewall settings blocking the required ports like (5353/udp). 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/375

Should I do what that link says or something else. I did remove and reinstall the HP after Xsane did not see it.

For a USB connected device, the firewall advice is not applicable. Check that the user is a member of the 'lp' group (for r/w access to the USB interface).

FWIW, I recall a recent thread where a user described similar symptoms (scanning as root only), and reported the following workaround...
https://www.linuxquestions.org/quest...ml#post6083457

Printer/scanner has wireless connection. Not connected w/USB. Will from the HP to USB stick. Will not scan from the scanner to computer with wireless or Ethernet.

Ok, then it is worth checking the firewall. If active, try disabling it temporarily, and attempt to scan.

Also you should know that in order for the hpaio (scanner backend) to function, the printer URI must be configured to use the 'hp' CUPS backend. That can be checked using
The 'hp-setup' utility should be capable of discovering and configuring the network-attached multifunction device.

What firewall? Where is the Firewall? How do I check it? I am using Linksys WRT54 G wireless router. It is totally open. (I am in remote location)

$ lpstat -t
scheduler is running
system default destination: HP-OfficeJet-Pro-6970
device for HP-OfficeJet-Pro-6970: dnssd://HP%20OfficeJet%20Pro%206970%20%5BD79C4B%5D._ipp._tcp.local/?uuid=d7a2558b-5629-7026-ff06-efca17342cb6
device for XP-400-Series: http://localhost:631/admin
HP-OfficeJet-Pro-6970 accepting requests since Wed 05 Feb 2020 01:52:55 PM CST
XP-400-Series accepting requests since Mon 21 May 2018 11:24:39 AM CDT
printer HP-OfficeJet-Pro-6970 is idle. enabled since Wed 05 Feb 2020 01:52:55 PM CST
printer XP-400-Series disabled since Mon 21 May 2018 11:24:39 AM CDT -
Rendering completed

How do I run the 'hp-setup' utility?

There may be an icon for it in your menu. Otherwise, open a terminal and type...

May need to add user to the scanner group.

This link may also help troubleshoot: https://wiki.debian.org/Scanner

BTW, the lpstat output you shared confirms that the CUPS dnssd backend is being used....
That utilises Avahi 'auto-discovery', and while that is suitable for most network printers, I think you'll need to use the HPLIP utilities (eg hp-setup) to configure CUPS with the appropriate 'hp' URI. It should look more like this....
Once that is configured correctly, you'll likely find that the hpaio (scanner backend) works too.