Not able to add community repo in Repo Management. (redefined after more debug)

Clean greenfield install of Automation Hub and upgrade of Ansible Tower instance with the new install script. No issues. Added rh-certified repo without any problems. Created custom namespace, and added customer collection, no problem.

Adding community repo under Repo Management fail with 520 errors, if requirements.yml contains collections/namespaces already present via rh-certified.

Example for fail:

URL https://galaxy.ansible.com/api/v2/collections/

requirements.yml:
collections:
  - name: vmware.vmware_rest
    source: https://galaxy.ansible.com
    version: 1.0.1
Save and sync gives the following output:

520, message='', url=URL('https://galaxy.ansible.com/api/v2/collections/vmware/vmware_rest/versions/0.1.1-dev70/docs-blob/')

Any namespace/collection not present in rh-certified defined in requirements.yml, will lead to successful add of community repo.