Can only docker login fron certain hosts

Hello all
I am running gitlab in a docker container with jwilder/nginx-proxy as described in github.com/psct/gitfab (readme only in german) on a host in the internet.

After creating a user I am able to docker login to the registry from my local Linux machine (behind NAT firewall), but neither from the host gitlab is running on nor from another host with full intenet connection.

I would be thankful for any hint where to look for further information on what might happen here.

King regards

Stephan

Log entry when fail:

==> /var/log/gitlab/registry/current <==
2017-12-03_11:12:09.16740 time=“2017-12-03T11:12:09.16731871Z” level=warning msg=“error authorizing context:
authorization token required” environment=production go.version=go1.8.1 http.request.host=registry.ovh.relinux.org
http.request.id=2ba54d3f-470d-41c9-948d-384a78107a21 http.request.method=GET http.request.remoteaddr=79.226.58.155 http.request.uri="/v2/" http.request.useragent=“docker/17.09.0-ce go/go1.8.3 git-commit/afdb6d4 kernel/4.14.0-rc3 os/linux arch/amd64 UpstreamClient(Docker-Client/17.09.0-ce \(linux\))” instance.id=5b6f717b-3097-4a00-81c6-50b1d98373f9 service=registry version=v2.6.1-1-gdd544a8
2017-12-03_11:12:09.16748 127.0.0.1 - - [03/Dec/2017:11:12:09 +0000] “GET /v2/ HTTP/1.0” 401 87 “” “docker/17.09.0-ce go/go1.8.3 git-commit/afdb6d4 kernel/4.14.0-rc3 os/linux arch/amd64 UpstreamClient(Docker-Client/17.09.0-ce \(linux\))”

==> /var/log/gitlab/nginx/gitlab_registry_access.log <==
172.19.0.3 - - [03/Dec/2017:11:12:09 +0000] “GET /v2/ HTTP/1.1” 401 87 “” “docker/17.09.0-ce go/go1.8.3 git-commit/afdb6d4 kernel/4.14.0-rc3 os/linux arch/amd64 UpstreamClient(Docker-Client/17.09.0-ce \x5C(linux\x5C))”

==> /var/log/gitlab/gitlab-rails/production.log <==
Started GET “/jwt/auth?account=stephan&client_id=docker&offline_token=[FILTERED]&service=container_registry” for 172.19.0.3 at 2017-12-03 11:12:09 +0000
Processing by JwtController#auth as HTML
Parameters: {“account”=>“stephan”, “client_id”=>“docker”, “offline_token”=>"[FILTERED]", “service”=>“container_registry”}