Issue running vyos-1.3 on Docker

When I execute this on an Ubuntu 18.04 instance:

sudo docker build --compress -f Dockerfile -t vyos:1.3 --build-arg BUILD_DATE="`date -u --rfc-3339=seconds`" --build-arg VYOS_VERSION=1.3 --build-arg DEBIAN_VERSION=buster --progress plain ..

I see these kinds of errors:

Get:12 http://repo.powerdns.com/debian bullseye-rec-45 InRelease [1798 B]
Err:12 http://repo.powerdns.com/debian bullseye-rec-45 InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1B0C6205FD380FBB
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/vyos.list:9
W: https://repos.influxdata.com/debian/dists/bullseye/Release: No system certificates available. Try installing ca-certificates.
W: https://repo.saltproject.io/py3/debian/11/amd64/3004/dists/bullseye/Release: No system certificates available. Try installing ca-certificates.
W: GPG error: http://repo.powerdns.com/debian bullseye-rec-45 InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 1B0C6205FD380FBB
E: The repository 'http://repo.powerdns.com/debian bullseye-rec-45 InRelease' is not signed.
E: The repository 'https://repos.influxdata.com/debian bullseye Release' does not have a Release file.
E: The repository 'https://repo.saltproject.io/py3/debian/11/amd64/3004 bullseye Release' does not have a Release file.
dpkg: warning: ignoring request to remove dosfstools which isn't installed
/tmp/hooks/18-enable-disable_services.chroot: 4: /tmp/hooks/18-enable-disable_services.chroot: systemctl: not found

I then end up with a small (81.3MB) image that doesn’t really run.

Please can someone advise/help? Appears the scripts are trying to install the latest (bullseye) versions of some packages, although I have defined DEBIAN_VERSION as buster.

I see that the defaults.json file refers to bullseye. Does it need to be updated for buster?