Actually this was exactly what happened and surprised me. I was moving my blog out of GitHub Pages to a self-hosted solution, and it's only after switching DNS

Actually this was exactly what happened and surprised me. I was moving my blog out of GitHub Pages to a self-hosted solution, and it's only after switching DNS and generating the cert for my own server that I noticed that GH Pages was ALSO serving the old version of the blog over HTTPS. I didn't know about LE revocation mechanism at the time.