Pages custom domain: InvalidDNSError and Dnsruby::ServFail, while Google and Cloudflare resolve correctly

[papakult]

Hello! We cannot obtain a GitHub Pages HTTPS certificate for zolotaya-vilka.ru. Repository: https://github.com/papakult/zolotaya-vilka. Deployment uses GitHub Actions and completes successfully. HTTP serves the site, but HTTPS presents a *.github.io certificate that does not cover the custom domain.

DNS configuration: nameservers ns1.reg.ru and ns2.reg.ru; apex A records 185.199.108.153, 185.199.109.153, 185.199.110.153, 185.199.111.153; www CNAME papakult.github.io. Google Public DNS and Cloudflare return these records. Apex AAAA, CAA and DS queries return no records without an error.

The Pages health API reported dns_resolves=false, is_https_eligible=false, InvalidDNSError (Domain's DNS record could not be retrieved), and caa_error=Dnsruby::ServFail for the apex and www. The UI shows DNS check unsuccessful.

We have removed and re-added the custom domain and redeployed successfully, but HTTPS is still unavailable. There is a separate light-version repository using Vercel; Pages is not enabled there, and the custom domain is configured on the main repository only. We have also opened a ticket with the DNS provider.

How can we determine which DNS lookup is failing for GitHub's resolver? Is there a known issue with REG.RU authoritative DNS or a way to get more detailed Pages DNS diagnostics? We would appreciate a specific diagnostic step before changing nameservers or hosting.

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