Can't create new Project and no Error message

Hi. I’ve been following the instruction on enabling GitLab Pages:
https://docs.gitlab.com/ee/administration/pages/index.htm

to set up GitLab Pages on my self-hosted instance. However, when I try to actually create any type of Pages project from a Template, I keep getting the following error:

How can I diagnose the problem? I’m not getting any errors from gitlab-ctl reconfigure.