GitLab Pages: Problem with HTML files artifacts

We are selfhosting GitLab at a domain https://git.example.com. Our GitLab Pages are under https://pages.example.com.

If a user now tries to get an HTML from an artifact

https://group.pages.example.com/-/projects/-/jobs/687990/artifacts/public/index.html it leads to an 502 error.

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

{"error":"Get https://git.example.com/api/v4/projects/group%2Fproject/jobs/687990/artifacts/public/index.html: dial tcp: lookup git.example.com on [::1]:53: read udp [::1]:35773-\u003e[::1]:53: read: connection refused","host":"group.pages.example.com","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: https://git.example.com
GitLab Pages URL: https://pages.example.com (Wildcard TLS)
GitLab Registry: https://registry.git.example.com