Missing Duplex Configuration with HPLIP 3.17.10 in Ubuntu 18.04LTS

[Jens Scheffler]

Hi HP Team,
I have an HP Color LaserJet Pro M477fdw and have Ubuntu 18.04LTS installed and a print driver using CPUS/HPLIP installed.
Al is working fine just I am NOT able to select whether duplex is used or not. There is one duplex option in the printer preferences and print details dialog but disabled.

How can the option being turned on?

jscheffl@hp840g1:~$ dpkg -l|grep hp
ii hplip 3.17.10+repack0-5 amd64 HP Linux Printing and Imaging System (HPLIP)
ii hplip-data 3.17.10+repack0-5 all HP Linux Printing and Imaging - data files

Thanks,
Jens

P.S.:
jscheffl@hp840g1:~$ hp-doctor
Traceback (most recent call last):
  File "/usr/bin/hp-doctor", line 42, in <module>
    check_extension_module_env('cupsext')
  File "/usr/share/hplip/base/g.py", line 339, in check_extension_module_env
    python_ver = xint((sys.version).split(' ')[0]) #find the current python version ; xint() to convert string to int, returns a list
  File "/usr/share/hplip/base/g.py", line 331, in xint
    return l
UnboundLocalError: local variable 'l' referenced before assignment
--> Running the script with python3 manually made it better but even after installing a couple of additional modules the options & features in the print preferenced did not enhance.

[Jens Scheffler (jscheffl)]

jscheffl@hp840g1:~$ python3 /usr/share/hplip/doctor.py

HP Linux Imaging and Printing System (ver. 3.17.10)
Self Diagnse Utility and Healing Utility ver. 1.0

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.

HP Linux Imaging and Printing System (ver. 3.17.10)
Self Diagnse Utility and Healing Utility ver. 1.0

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.

Checking for Deprecated items....
error: This distro (i.e ubuntu 18.04) is either deprecated or not yet supported.
The diagnosis is limited on unsupported platforms. Do you want to continue?(y=yes*, n=no):y

Checking for HPLIP updates....
error: Failed to locate hp-upgrade utility

Checking for Dependencies....
warning: 12-18.04 version is not supported. Using 12-17.04 versions dependencies to verify and install...

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

 Kernel: 4.15.0-43-generic #46-Ubuntu SMP Thu Dec 6 14:45:28 UTC 2018 GNU/Linux
 Host: hp840g1
 Proc: 4.15.0-43-generic #46-Ubuntu SMP Thu Dec 6 14:45:28 UTC 2018 GNU/Linux
 Distribution: 12 18.04
 Bitness: 64 bit

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

HPLIP-Version: HPLIP 3.17.10
HPLIP-Home: /usr/share/hplip
warning: HPLIP-Installation: Auto installation is not supported for 12 distro 18.04 version

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

[hplip]
version=3.17.10

[dirs]
home=/usr/share/hplip
run=/var/run
ppd=/usr/share/ppd/hplip/HP
ppdbase=/usr/share/ppd/hplip
doc=/usr/share/doc/hplip
html=/usr/share/doc/hplip-doc
icon=no
cupsbackend=/usr/lib/cups/backend
cupsfilter=/usr/lib/cups/filter
drv=/usr/share/cups/drv
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=yes
gui-build=yes
scanner-build=yes
fax-build=yes
dbus-build=yes
cups11-build=no
doc-build=yes
shadow-build=no
hpijs-install=yes
foomatic-drv-install=yes
foomatic-ppd-install=yes
foomatic-rip-hplip-install=no
hpcups-install=yes
cups-drv-install=yes
cups-ppd-install=no
internal-tag=3.17.10
restricted-build=no
ui-toolkit=qt5
qt3=no
qt4=no
qt5=yes
policy-kit=yes
lite-build=no
udev_sysfs_rules=no
hpcups-only-build=no
hpijs-only-build=no
apparmor_build=no

Current contents of '/var/lib/hp/hplip.state' file:
[plugin]
installed = 1
eula = 1
version = 3.17.10

Current contents of '~/.hplip/hplip.conf' file:
[last_used]
device_uri = hpfax:/net/HP_Color_LaserJet_MFP_M477fdw?hostname=laser.local

[installation]
date_time = 01/20/19 20:51:02
version = 3.17.10

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

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

 cups CUPS - Common Unix Printing System ...