GitLab API access: FAILED. code: 502 (workhorse issue?) FIXED

For some reason Gitlab stopped working. I did not touch this installation for more then a year and need some help. Right now I cannot acces Gitlab, the website returns a 502 error and the selfcheck fails on the GitLab Shell. I have re-installed the Gitlab-Shell but that did not fix the issue. In the mean time I also upgrade a .point release to 8.3. e dare not to proceed with upgrading until I understand the current problem

[root@gitlab nginx]# tail -20 gitlab_error.log

2017/10/17 15:21:36 [error] 2087#2087: *137 connect() to unix:/home/git/gitlab/tmp/sockets/gitlab-workhorse.socket failed (111: Connection refused) while connecting to upstream, client:, server:, request: “POST /api/v3/internal/allowed HTTP/1.1”, upstream: “http://unix:/home/git/gitlab/tmp/sockets/gitlab-workhorse.socket:/api/v3/internal/allowed”, host: “”`

[root@gitlab gitlab]# sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production

System information
Current User:   git
Using RVM:      yes
RVM Version:    1.21.0
Ruby Version:   2.3.5p376
Gem Version:
Bundler Version:1.15.4
Rake Version:   10.5.0
Sidekiq Version:4.0.1

GitLab information
Version:        8.4.11
Revision:       e9bef8930d
Directory:      /home/git/gitlab
DB Adapter:     mysql2
SSH Clone URL:
Using LDAP:     yes
Using Omniauth: yes
Omniauth Providers: github, crowd

GitLab Shell
Version:        2.6.10
Repositories:   /home/git/repositories/
Hooks:          /home/git/gitlab-shell/hooks/
Git:            /usr/local/bin/git

[root@gitlab gitlab]# sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production

Checking GitLab Shell ...

GitLab Shell version >= 2.6.10 ? ... OK (2.6.10)
Repo base directory exists? ... yes
Repo base directory is a symlink? ... no
Repo base owned by git:git? ... yes
Repo base access is drwxrws---? ... yes
hooks directories in repos are links: ...
Running /home/git/gitlab-shell/bin/check
Check GitLab API access: FAILED. code: 502
gitlab-shell self-check failed
  Try fixing it:
  Make sure GitLab is running;
  Check the gitlab-shell configuration file:
  sudo -u git -H editor /home/git/gitlab-shell/config.yml
  Please fix the error above and rerun the checks.

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
Checking LDAP ... Finished

Checking GitLab ...

Git configured with autocrlf=input? ... yes
Database config exists? ... yes
Database is SQLite ... no
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? ... yes
Init script exists? ... yes
Init script up-to-date? ... yes
projects have namespace: ...
formatron ... no
  Try fixing it:
  Migrate global projects
  For more information see:
  doc/update/ in section "#global-projects"
  Please fix the error above and rerun the checks.
Redis version >= 2.8.0? ... yes
Ruby version >= 2.1.0 ? ... yes (2.3.5)
Your git bin path is "/usr/local/bin/git"
Git version >= 1.7.10 ? ... yes (2.14.2)
Active users: 220

Checking GitLab ... Finished

[root@gitlab gitlab-shell]# cat gitlab-shell.log

E, [2017-10-17T11:26:50.719588 #20190] ERROR -- : API call <POST> failed: 502 => <<html>
<head><title>502 Bad Gateway</title></head>
<body bgcolor="white">
<center><h1>502 Bad Gateway</h1></center>
W, [2017-10-17T11:26:50.719719 #20190]  WARN -- : gitlab-shell: Access denied for git command <git-upload-pack 'helios/helios-axiros.git'> by user with key key-16.

Any advise is greatly appreciated!!

It seems the rootcause was a corrupted /etc/default/gitlab file
cp /home/git/gitlab/lib/support/init.d/gitlab.default.example /etc/default/gitlab