update_security_db.sh script fails with "Network is unreachable" error behind proxy

First of all, due to this bug[0], landscape is deployed with the http(s)-proxy model-config instead of juju-http(s)-proxy.

The deployment of landscape-scalable bundle will successfully complete.
However, on the landscape dashboard, I do see one alert on the bottom as
"1 Landscape script has issues: 1 didn't run"
which is update_security_db.sh.

When I run this script manually on landscape-server unit, I do see the following error(added "set -x" in the script file in order to see the error).

$ sudo -u landscape /opt/canonical/landscape/script/update_security_db.sh
--- EXCERPT OUTPUT ---
+ logger -p info -t update-security-db -- ' % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
  0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
curl: (7) Failed to connect to usn.ubuntu.com port 443 after 304 ms: Network is unreachable'
+ exit 1
+ release_lock update_security_db.sh
+ get_distributed_lock update_security_db.sh --release
+ local command=/opt/canonical/landscape/get-distributed-lock
+ /opt/canonical/landscape/get-distributed-lock update_security_db.sh --release
+ rm -f /var/lock/update_security.lock

However, when I run this without specifying the landscape user, the script will complete without any errors.
It looks like the proxy configuration from model-config is not properly used with the landscape user.

The workaround I found is to configure the "Proxy for HTTP and HTTPS traffic" from the Landscape Web UI.
I have tried by configuring via charm config[1], but that did not help unfortunately.

[0] https://bugs.launchpad.net/landscape-charm/+bug/2025978
[1] https://charmhub.io/landscape-client/configurations#http-proxy