fax driver lost connection with printer

Kubuntu 19.10

HPLIP installed by download from HP site

The printer has a wired ethernet connection. (I tried also with usb connection, and I had the same issue)

I am trying to run print-to-fax, and it used to work, but now I am getting error messages. Removing and re-adding the printer doesn't help.

Let me mention that Windows has no trouble running print-to-fax jobs on this printer, using "HP Universal Fax Driver", so I don't think the problem lies with the printer.

The HPLIP troubleshooter says (I pasted the most relevant section first):

error: Unable to communicate with device (code=12): hpfax:/net/Officejet_Pro_6830?ip=XXX
error: unable to open channel
error: Communication status: Failed
HP Linux Imaging and Printing System (ver. 3.19.12)
Self Diagnse Utility and Healing Utility ver. 1.0

Copyright (c) 2001-18 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.

HP Linux Imaging and Printing System (ver. 3.19.12)
Self Diagnse Utility and Healing Utility ver. 1.0

Copyright (c) 2001-18 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.

Checking for Deprecated items....
No Deprecated items are found

Checking for HPLIP updates....

HP Linux Imaging and Printing System (ver. 3.19.12)
HPLIP upgrade latest version ver. 1.0

Copyright (c) 2001-18 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.

Latest version of HPLIP is already installed.

Checking for Dependencies....

---------------
| SYSTEM INFO |
---------------

 Kernel: 5.3.0-26-generic #28-Ubuntu SMP Wed Dec 18 05:37:46 UTC 2019 GNU/Linux
 Host: shmuel-Kubuntu
 Proc: 5.3.0-26-generic #28-Ubuntu SMP Wed Dec 18 05:37:46 UTC 2019 GNU/Linux
 Distribution: 12 19.10
 Bitness: 64 bit

-----------------------
| HPLIP CONFIGURATION |
-----------------------

HPLIP-Version: HPLIP 3.19.12
HPLIP-Home: /usr/share/hplip
HPLIP-Installation: Auto installation is supported for ubuntu distro 19.10 version

Current contents of '/etc/hp/hplip.conf' file:
# hplip.conf. Generated from hplip.conf.in by configure.

[hplip]
version=3.19.12

[dirs]
home=/usr/share/hplip
run=/var/run
ppd=/usr/share/ppd/HP
ppdbase=/usr/share/ppd
doc=/usr/share/doc/hplip-3.19.12
html=/usr/share/doc/hplip-3.19.12
icon=/usr/share/applications
cupsbackend=/usr/lib/cups/backend
cupsfilter=/usr/lib/cups/filter
drv=/usr/share/cups/drv/hp
bin=/usr/bin
apparmor=/etc/apparmor.d
# Following values are determined at configure time and cannot be changed.
[configure]
network-build=yes
libusb01-build=no
pp-build=no
gui-build=yes
scanner-build=yes
fax-build=yes
dbus-build=yes
cups11-build=no
doc-build=yes
shadow-build=no
hpijs-install=no
foomatic-drv-install=no
foomatic-ppd-install=no
foomatic-rip-hplip-install=no
hpcups-install=yes
cups-drv-install=yes
cups-ppd-install=no
internal-tag=3.19.12
restricted-build=no
ui-toolkit=qt4
qt3=no
qt4=yes
qt5=no
policy-kit=no
lite-build=no
udev_sysfs_rules=no
hpcups-only-build=no
hpijs-only-build=no
apparmor_build=yes
class-driver=no

Current contents of '/var/lib/hp/hplip.state' file:
Plugins are not installed. Could not access file: No such file or directory

Current contents of '~/.hplip/hplip.conf' file:
[upgrade]
latest_available_version = 3.17.10
notify_upgrade = true
last_upgraded_time = 1578252103
pending_upgrade_time = 0

[settings]
systray_visible = 0
systray_messages = 2

[last_used]
device_uri = "hpfax:/net/Officejet_Pro_6830?ip=XXX"
printer_name = Officejet_Pro_6830_fax
working_dir = .

[commands]
scan = /usr/bin/xsane -V %SANE_URI%

[refresh]
rate = 30
enable = false
type = 1

[polling]
enable = false
interval = 5
device_list =

[fax]
voice_phone =
email_address =

[installation]
date_time = 01/14/20 09:20:14
version = 3.19.12

 <Package-name> <Package-Desc> <Required/Optional> <Min-Version> <Installed-Version> <Status> <Comment>

-------------------------
| External Dependencies |
-------------------------

 cups CUPS - Common Unix Printing System REQUIRED 1.1 2.2.12 OK 'CUPS Scheduler is running'
 gs GhostScript - PostScript and PDF language interpreter and previewer REQUIRED 7.05 9.27 OK -
 xsane xsane - Graphical scanner frontend for SANE OPTIONAL 0.9 0.999 OK -
 scanimage scanimage - Shell scanning program OPTIONAL 1.0 1.0.27 OK -
 dbus DBus - Message bus system REQUIRED - 1.12.14 OK -
 policykit PolicyKit - Administrative policy framework OPTIONAL - 0.105 OK -
 network network -wget OPTIONAL - 1.20.3 OK -
 avahi-utils avahi-utils OPTIONAL - 0.7 OK -

------------------------
| General Dependencies |
------------------------

 libjpeg libjpeg - JPEG library REQUIRED - - OK -
 cups-devel CUPS devel- Common Unix Printing System development files REQUIRED - 2.2.12 OK -
 cups-image CUPS image - CUPS image development files REQUIRED - 2.2.12 OK -
 libpthread libpthread - POSIX threads library REQUIRED - b'2.30' OK -
 libusb libusb - USB library REQUIRED - 1.0 OK -
 sane SANE - Scanning library REQUIRED - - OK -
 sane-devel SANE - Scanning library development files REQUIRED - - OK -
 libnetsnmp-devel libnetsnmp-devel - SNMP networking library development files REQUIRED 5.0.9 5.7.3 OK -
 libcrypto libcrypto - OpenSSL cryptographic library REQUIRED - 1.1.1 OK -
 python3X Python 2.2 or greater - Python programming language REQUIRED 2.2 3.7.5 OK -
 python3-notify2 Python libnotify - Python bindings for the libnotify Desktop notifications OPTIONAL - - OK -
 python3-pyqt4-dbus PyQt 4 DBus - DBus Support for PyQt4 OPTIONAL 4.0 4.12.1 OK -
 python3-pyqt4 PyQt 4- Qt interface for Python (for Qt version 4.x) REQUIRED 4.0 4.12.1 OK -
 python3-dbus Python DBus - Python bindings for DBus REQUIRED 0.80.0 1.2.12 OK -
 python3-xml Python XML libraries REQUIRED - 2.2.7 OK -
 python3-devel Python devel - Python development files REQUIRED 2.2 3.7.5 OK -
 python3-pil PIL - Python Imaging Library (required for commandline scanning with hp-scan) OPTIONAL - 6.1.0 OK -
 python3-reportlab Reportlab - PDF library for Python OPTIONAL 2.0 3.5.23 OK -

--------------
| COMPILEDEP |
--------------

 libtool libtool - Library building support services REQUIRED - 2.4.6 OK -
 gcc gcc - GNU Project C and C++ Compiler REQUIRED - 9.2.1 OK -
 make make - GNU make utility to maintain groups of programs REQUIRED 3.0 4.2.1 OK -

---------------------
| Python Extentions |
---------------------

 cupsext CUPS-Extension REQUIRED - 3.19.12 OK -
 hpmudext IO-Extension REQUIRED - 3.19.12 OK -

----------------------
| Scan Configuration |
----------------------

 hpaio HPLIP-SANE-Backend REQUIRED - 3.19.12 OK 'hpaio found in /etc/sane.d/dll.conf'
 scanext Scan-SANE-Extension REQUIRED - 3.19.12 OK -

------------------------------
| DISCOVERED SCANNER DEVICES |
------------------------------

device `hpaio:/net/officejet_pro_6830?ip=XXX&queue=false' is a Hewlett-Packard officejet_pro_6830 all-in-one

--------------------------
| DISCOVERED USB DEVICES |
--------------------------

No devices found.

---------------------------------
| INSTALLED CUPS PRINTER QUEUES |
---------------------------------

HP_Officejet_Pro_6830_C9CB08_
-----------------------------
Type: Unknown
Device URI: implicitclass://HP_Officejet_Pro_6830_C9CB08_/
PPD: /etc/cups/ppd/HP_Officejet_Pro_6830_C9CB08_.ppd
warning: Failed to read /etc/cups/ppd/HP_Officejet_Pro_6830_C9CB08_.ppd ppd file
PPD Description:
Printer status: printer HP_Officejet_Pro_6830_C9CB08_ is idle. enabled since Tue 14 Jan 2020 08:42:14 AM IST
warning: Printer is not HPLIP installed. Printers must use the hp: or hpfax: CUPS backend for HP-Devices.

Officejet_Pro_6830_fax
----------------------
Type: Fax
Device URI: hpfax:/net/Officejet_Pro_6830?ip=XXX
PPD: /etc/cups/ppd/Officejet_Pro_6830_fax.ppd
warning: Failed to read /etc/cups/ppd/Officejet_Pro_6830_fax.ppd ppd file
PPD Description:
Printer status: printer Officejet_Pro_6830_fax is idle. enabled since Fri 10 Jan 2020 09:54:06 AM IST
error: Unable to communicate with device (code=12): hpfax:/net/Officejet_Pro_6830?ip=XXX
error: unable to open channel
error: Communication status: Failed

--------------
| PERMISSION |
--------------

Checking Permissions....

Checking for Configured Queues....
warning: Fail to read ppd=/etc/cups/ppd/HP_Officejet_Pro_6830_C9CB08_.ppd file
warning: Insufficient permission to access file /etc/cups/ppd/HP_Officejet_Pro_6830_C9CB08_.ppd
warning: Could not complete Queue(s) configuration check

Checking for HP Properitery Plugin's....
No plug-in printers are configured.

Checking for Printer Status....
error: 'Officejet_Pro_6830_fax' Printer is either Powered-OFF or Failed to communicate.
Turn On Printer and re-run hp-doctor

Diagnose completed...

More information on Troubleshooting,How-To's and Support is available on http://hplipopensource.com/hplip-web/index.html

Please close this terminal manually.