Docker pull from remote smart-proxy fails

Problem:
Try to pull Docker image from remote smart-proxy does not succeed. A pull from the main Foreman server works.

Expected outcome:
Pull an image from the remote smart-proxy.

Foreman and Proxy versions:
Foreman 1.23.1

Foreman and Proxy plugin versions:

Distribution and version:
CentOS 7

Other relevant data:

==> /var/log/httpd/crane_access_ssl.log <==
172.18.3.226 - - [21/Nov/2019:10:30:37 -0800] "GET /v2/ HTTP/1.1" 200 2 "-" "docker/19.03.5 go/go1.12.12 git-commit/633a0ea kernel/3.10.0-1062.4.3.el7.x86_64 os/linux arch/amd64 UpstreamClient(Docker-Client/19.03.5 \\(linux\\))"
172.18.3.226 - - [21/Nov/2019:10:30:37 -0800] "GET /v2/sdsc-hci-production-percona_pmm_server_docker_images-percona_pmm_server-docker_pmm_server/manifests/2.0.0 HTTP/1.1" 404 53 "-" "docker/19.03.5 go/go1.12.12 git-commit/633a0ea kernel/3.10.0-1062.4.3.el7.x86_64 os/linux arch/amd64 UpstreamClient(Docker-Client/19.03.5 \\(linux\\))"

The Foreman server has “tfm-rubygem-pulp_docker_client” installed and the smart-proxy does not. From the error messages, this may be needed. Foreman also has “tfm-rubygem-foreman_docker” and tfm-rubygem-hammer_cli_foreman_docker" installed, but these seem less likely.

Is the smart proxy assigned to the correct lifecycle enviroment (on the smart proxy edit page)?
Were you able to sync the smart proxy without error?

Yes, it is assigned to the correct lifecycle environment and the smart proxy has been syncing nightly without error.
The result of a “docker pull” from a host registered to the remote smart proxy is:
“Error response from daemon: unknown: Not Found”
The same host will pull directly from Foreman. (a firewall exception was temporarily allowed to test this)