Gitlab container registry failed to login on remote hosts

Infrastructure as Code & Cloud Native
1

Hello,
I’m trying to configure a self-hosted gitlab to be a container registry. I’m launching with this docker-compose:

services:
 web:
  image: gitlab/gitlab-ce:13.3.5-ce.0
  hostname: gitlab.mycompany.com
  extra_hosts:
    - email.mycompany.com:192.168.51.25
  environment:
    GITLAB_OMNIBUS_CONFIG: |
      external_url 'https://gitlab.mycompany.com:10443'
      letsencrypt['enable'] = false
      registry_external_url 'https://gitlab.mycompany.com:15050'
      gitlab_rails['smtp_enable'] = true
      gitlab_rails['smtp_address'] = 'email.mycompany.com'
      gitlab_rails['smtp_port'] = 25
      gitlab_rails['smtp_domain'] = 'mycompany.com'
      gitlab_rails['smtp_tls'] = false
      gitlab_rails['smtp_openssl_verify_mode'] = 'none'
      gitlab_rails['smtp_enable_starttls_auto'] = false
      gitlab_rails['smtp_ssl'] = false
      gitlab_rails['smtp_force_ssl'] = false
      gitlab_rails['packages_enabled'] = true
  ports:
    - "10443:10443"
    - "10022:22"
    - "15050:15050"

I have a valid certificate in /etc/gitlab/ssl and the gitlab website works like a charm when I go to https://gitlab.mycompany.com:10443

For the container registry login, I’m facing this oddities:
on the host where the gitlab is running I can perform a docker login gitlab.mycompany.com:15050 , input my login/password and it works

Authenticating with existing credentials...
WARNING! Your password will be stored unencrypted in /root/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store

Login Succeeded

When I try to login from another host, with the same login/pasword it fails with this message:

Error response from daemon: Get https://gitlab.mycompany.com:15050/v2/: Forbidden

I found this earlier topic of someone who had the same problem but no hints where given ( Unable to login to gitlab container registry from another server )

Can somebody provides me with some hints of how I can diagnose my problem and maybe solve it ?