I use Disqus comment system. One thing puzzled me is that the comments did not show up sometimes, but sometimes it did. Finally I figured out it is because github pages treats “http” and “https” requests as the same. But Disqus treats them as two different URLs. So the comments are not visible to each other.

The fix is simple, just redirect “http” requests to “https”:

https://help.github.com/articles/securing-your-github-pages-site-with-https/