GitLab Pages: Problem with HTML files artifacts

We are selfhosting GitLab at a domain Our GitLab Pages are under

If a user now tries to get an HTML from an artifact it leads to an 502 error.

In the /var/log/gitlab-pages/current file:

{"error":"Get dial tcp: lookup on [::1]:53: read udp [::1]:35773-\u003e[::1]:53: read: connection refused","host":"","level":"error","msg":"Failed to request the artifact","path":"/-/project/-/jobs/687990/artifacts/public/index.html","time":"2020-03-02T14:07:23Z"}

It seems to be an DNS Lookup error. Any ideas how to fix this?

GitLab Version: 12.7.6 EE
OS: Centos 7.7.1908 (core)
GitLab URL:
GitLab Pages URL: (Wildcard TLS)
GitLab Registry: