Docker push to private registry fails and makes runner (including new register) stuck

Summary

Docker push to my private registry fails with 'unauthorized: HTTP Basic: Access denied'. When I retry the build after that error the (shell) runner doesn't show any output. And is stuck in the state 'pending'. When I try to add a new runner the registration fails with:

ERROR: Registering runner... forbidden (check registration token)  runner=pG7EYAYe**
PANIC: Failed to register this runner. Perhaps you are having network problems

There isn't a network problem and even after a GitLab token reset this error persists.

GitLab Outputs / Reproduce

docker push mysite:4567/myuser/myproject/postgres
```
fails with
```bash
$ docker push mysite:4567/myuser/myproject/postgres
The push refers to a repository [mysite:4567/myuser/myproject/postgres]
efcfc1afd54c: Preparing
ed392489b9a1: Preparing
5112d1f5d6cc: Preparing
c43e90ccc3cb: Preparing
9489cc92de20: Preparing
1df293743ebf: Preparing
76499c539635: Preparing
42f4e8cac5cb: Preparing
6fd1c77ca76a: Preparing
ab7eb640bee4: Preparing
b0b5387b073d: Preparing
57655c1c901b: Preparing
0df5ee6f45b1: Preparing
70df7c5241b7: Preparing
dd30fd70f347: Preparing
73c4fa66091a: Preparing
142a601d9793: Preparing
1df293743ebf: Waiting
76499c539635: Waiting
42f4e8cac5cb: Waiting
6fd1c77ca76a: Waiting
ab7eb640bee4: Waiting
b0b5387b073d: Waiting
57655c1c901b: Waiting
0df5ee6f45b1: Waiting
70df7c5241b7: Waiting
dd30fd70f347: Waiting
73c4fa66091a: Waiting
142a601d9793: Waiting
unauthorized: HTTP Basic: Access denied
ERROR: Build failed: exit status 1
```
##  .gitlab-ci.yml Stage
I am not sure if I am handling this right here. Since I have a docker-compose setup I want to add all those multiple containers/images to the registry of my project. E.g. the postgres, django, redis container etc. (See the last two lines).
```bash
build:
  script:
     - docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN mysite:4567/myuser/myproject
     - docker-compose -f dev.yml build 
     - docker tag envis_postgres mysite:4567/myuser/myproject/postgres
     - docker push mysite:4567/myuser/myproject/postgres
```
### Output of checks

#### Results of GitLab application Check
``` bash
Checking GitLab Shell ...

GitLab Shell version >= 3.6.1 ? ... OK (3.6.1)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ...
6/5 ... ok
6/6 ... ok
6/8 ... repository is empty
6/12 ... ok
12/19 ... ok
12/20 ... ok
16/21 ... ok
17/22 ... ok
18/23 ... ok
18/24 ... ok
18/25 ... ok
18/26 ... ok
21/27 ... ok
18/28 ... ok
22/31 ... ok
12/32 ... ok
21/34 ... repository is empty
6/35 ... ok
17/36 ... ok
22/37 ... ok
6/38 ... ok
12/39 ... ok
21/40 ... ok
6/41 ... ok
16/43 ... ok
17/44 ... ok
22/45 ... ok
24/46 ... ok
12/47 ... ok
6/48 ... ok
16/49 ... ok
25/50 ... ok
6/51 ... ok
24/53 ... ok
33/54 ... ok
12/55 ... ok
18/57 ... ok
22/60 ... ok
24/61 ... ok
22/62 ... ok
24/64 ... ok
34/65 ... ok
6/66 ... ok
22/67 ... ok
24/68 ... ok
24/70 ... ok
25/72 ... repository is empty
6/73 ... ok
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
Send ping to redis server: OK
gitlab-shell self-check successful

Checking GitLab Shell ... Finished

Checking Sidekiq ...

Running? ... yes
Number of Sidekiq processes ... 1

Checking Sidekiq ... Finished

Checking Reply by email ...

Reply by email is disabled in config/gitlab.yml

Checking Reply by email ... Finished

Checking LDAP ...

LDAP users with access to your GitLab server (only showing the first 100 results                                                        )
Server: ldapmain
	I HAVE REMOVE THAT HERE (shows user names and domain)

Checking LDAP ... Finished

Checking GitLab ...

Git configured with autocrlf=input? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config outdated? ... no
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory setup correctly? ... no
  Try fixing it:
  sudo chown -R git /var/opt/gitlab/gitlab-rails/uploads
  sudo find /var/opt/gitlab/gitlab-rails/uploads -type f -exec chmod 0644 {} \;
  sudo find /var/opt/gitlab/gitlab-rails/uploads -type d -not -path /var/opt/gitlab/gitlab-rails/uploads -exec chmod 0700 {} \;
  For more information see:
  doc/install/installation.md in section "GitLab"
  Please fix the error above and rerun the checks.
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
projects have namespace: ...
6/5 ... yes
6/6 ... yes
6/8 ... yes
6/12 ... yes
12/19 ... yes
12/20 ... yes
16/21 ... yes
17/22 ... yes
18/23 ... yes
18/24 ... yes
18/25 ... yes
18/26 ... yes
21/27 ... yes
18/28 ... yes
22/31 ... yes
12/32 ... yes
21/34 ... yes
6/35 ... yes
17/36 ... yes
22/37 ... yes
6/38 ... yes
12/39 ... yes
21/40 ... yes
6/41 ... yes
16/43 ... yes
17/44 ... yes
22/45 ... yes
24/46 ... yes
12/47 ... yes
6/48 ... yes
16/49 ... yes
25/50 ... yes
6/51 ... yes
24/53 ... yes
33/54 ... yes
12/55 ... yes
18/57 ... yes
22/60 ... yes
24/61 ... yes
22/62 ... yes
24/64 ... yes
34/65 ... yes
6/66 ... yes
22/67 ... yes
24/68 ... yes
24/70 ... yes
25/72 ... yes
6/73 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.1.0 ? ... yes (2.3.1)
Your git bin path is "/opt/gitlab/embedded/bin/git"
Git version >= 2.7.3 ? ... yes (2.7.4)
Active users: 14

Checking GitLab ... Finished
```

#### Results of GitLab environment info
```bash
System information
System:         Debian 7.11
Current User:   git
Using RVM:      no
Ruby Version:   2.3.1p112
Gem Version:    2.6.6
Bundler Version:1.13.1
Rake Version:   10.5.0
Sidekiq Version:4.1.4

GitLab information
Version:        8.12.6
Revision:       fa20b51
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
URL:            https://mysite.company.com
HTTP Clone URL: https://mysite.company.com/some-group/some-project.git
SSH Clone URL:  git@mysite.company.com:some-group/some-project.git
Using LDAP:     yes
Using Omniauth: no

GitLab Shell
Version:        3.6.1
Repository storage paths:
- default:      /var/opt/gitlab/git-data/repositories
Hooks:          /opt/gitlab/embedded/service/gitlab-shell/hooks/
Git:            /opt/gitlab/embedded/bin/git

```