Custom domain rollback bug

 I’m trying to serve my project page in github. The repository of project page is I first connected my custom domain with A record of DNS to this repository and it worked well. But, GitHub Pages warned me to use CNAME record so I changed to it. But after changing to CNAME record everytime I push to repository custom domain setting is gone so I have to reset custom domain. How can I fix this problem? Do I have to use A record for custom domain?

This error was caused by config error. I setup my baseURL to custom domain but it has to be set to github pages domain. I got email from github had error while building but I’d checked my email just now.

Edit. It was not config error. My CNAME record is pointing correctly but when I push github say is not.