Can't get LE's Cert for "Pages" when "Force HTTPS" enabled

Summary

Can't get LE's Cert for "Pages" when "Force HTTPS" enabled.

Steps to reproduce

1. Make sure "Force HTTPS" enabled
2. Add new custom domain, enable "Automatic certificate management using Let's Encrypt
3. Verify ownership of domain
4. Wait for LE cert generate forever

What is the current bug behavior?

LE cert will never generated.

What is the expected correct behavior?

LE cert be generated after 30m.

Output of checks

This bug happens on GitLab.com

Possible Workaround

remove domain, disable "Force HTTPS"，add domain and verify it, wait about 15min