The browser shown Not Secure when access GitLab Pages with custom domain+Let's Encrypt's cert

Summary

When access the user's Pages (already configured with TLS cert) by the custom sub-domain the client show Not Secure. The browser found certificate of GitLab instead of the upload one (Let's Encrypt);

Steps to reproduce

  • Create a user Pages. e.g. siritas.gitlab.io

  • Add a custom domain to the user Pages (press New Domain button) e.g. add domain by.dahoba.xyz to siritas.gitlab.io

    • also add a TLS certificate which generated with Let's Encrypt; Certificate (PEM) and Key (PEM) from fullchain.pem, privkey.pem accordingly.
    • press Create New Domain button

  • Add CNAME record

  • After dig command show that CNAME record was modified; like this:by.dahoba.xyz. ... IN CNAME siritas.gitlab.io.

Expected behavior

When access, the browser show the custom domain site was Secure. It should found the upload certificate.

Actual behavior

When access, the browser show the custom domain site was Not Secure;

Its found cert of gitlab instead of the uploaded one (Let's Encrypt).

Relevant logs and/or screenshots

Picture shown that I already add TLS cert information

Imgur

Result of dig command line

img

Picture shown that the website was Not Secure; Its found cert of gitlab instead of the uploaded one (Let's Encrypt).

Imgur

Output of checks

This bug happens on GitLab.com