Maybe it helps to reset the _default_cert.yml to use a self signed certificate? See also ns8-traefik/imageroot/actions/create-module/50create at 3249b89fb3812658d4cabc41e5c167976a5ea5dd · NethServer/ns8-traefik · GitHub
Please backup the system before or at least backup the original _default_cert.yml file, just in case something goes wrong.
Enter traefik environment:
runagent -m traefik1
Reset _default_cert.yml:
cat <<EOF > configs/_default_cert.yml
tls:
stores:
default:
defaultCertificate:
certFile: /etc/traefik/selfsigned.crt
keyFile: /etc/traefik/selfsigned.key
EOF