GitLab Pages returning Error 502 when in a specific subgroup

We are currently maintaining two major subgroups in our work. The Subgroup A is our internal subgroup and the GitLab Pages in the projects of that subgroup works fine.

However, when the same project from Subgroup A is forked to Subgroup B , the link from GitLab Pages returns an Error 502 “Whoops, something went wrong on our end” without any further error information.

Other notes: We are just using the GitLab from our web browsers; we do not use any further tools such as GitLab CE. We also tried looking at GitLab forums and cannot find entries similar to our case.