The same happened to me, I searched my CNAME on github and found that a user was "hijacking" some CNAMEs, pointing these domains to his own repos. This happened

The same happened to me, I searched my CNAME on github and found that a user was "hijacking" some CNAMEs, pointing these domains to his own repos. This happened to me because I switched from PRO to Free and I didn't notice that the Free plan does not allow us to have a private repository with Github Pages. The end result in my case is that I migrated my blog to Netlify and used Hugo to generate my HTML site from Markdown files. It was very straightforward and I am satisfied with the end result.