Socket Error: GitLab Pages on separate Server

Summary

We moved our GitLab Pages from a single GitLab Instance to a separate server following this docs https://docs.gitlab.com/ce/administration/pages/#running-gitlab-pages-in-a-separate-server First few days everything worked as expected, but since the last two days we see a 502 timeout error page without changing any settings. According to our logs the connection to gitlab-workhorse socket is refused. If I enable gitlab-workhorse within gitlab.rb or use the standard configuration the error remains, but an additional error shows up within gitlab-workhorse.

I found some related issues here, but nothing helped and those tickets are closed.

Relevant logs

==> /var/log/gitlab/nginx/gitlab_error.log <==
2019/06/28 09:23:52 [error] 7296#0: *365 connect() to unix:/var/opt/gitlab/gitlab-workhorse/socket failed (111: Connection refused) while connecting to upstream, client: xxxxx, server: xxxxx, request: "GET /oauth/authorize?client_id=69be92286bbf57071cf30386b190e7ab0b614c968ac0ac14e22d428cf485102e&redirect_uri=https://projects.pages.domain.de/auth&response_type=code&state=MFfcnPO6Eg38Nzh9OJ0vzg== HTTP/1.1", upstream: "http://unix:/var/opt/gitlab/gitlab-workhorse/socket:/oauth/authorize?client_id=69be92286bbf57071cf30386b190e7ab0b614c968ac0ac14e22d428cf485102e&redirect_uri=https://projects.pages.domain.de/auth&response_type=code&state=MFfcnPO6Eg38Nzh9OJ0vzg==", host: "xxxx"
==> /var/log/gitlab/gitlab-workhorse/current <==
2019-06-28_08:07:39.13120 time="2019-06-28T10:07:39+02:00" level=error msg=error correlation_id=nujG5r6mMC5 error="badgateway: failed after 0s: dial unix /var/opt/gitlab/gitlab-rails/sockets/gitlab.socket: connect: connection refused" method=GET uri=/

Details of package version

Provide the package version installation details

Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                                           Version                              Architecture                         Description
+++-==============================================================-====================================-====================================-=================================================================================================================================
un  gitlab-ce                                                                                                                    (no description available)
ii  gitlab-ee                                                      11.11.3-ee.0                         amd64                                GitLab Enterprise Edition (including NGINX, Postgres, Redis)

Environment details

Operating System: REPLACE-WITH-DETAILS
Installation Target, remove incorrect values:
- VM: Ubuntu 18.04.2 on ESXi Host
Installation Type, remove incorrect values:
- New Installation
Is there any other software running on the machine: No
Is this a single or multiple node installation? Single instance
Resources
- CPU: 2
- Memory total: 2GB