Comments not working on site with ssl

I am getting an unsecure error on Firefox and an empty content error on chrome on a site running on https:// protocol. When you click submit on standard comments on posts it shows an error with the URL as https://mysite…/site/wp-comments-post.php in the address bar. (My site is in a subdirectory).

I’ve gone through all the plugins and checked the theme and I can’t find the cause so I am assuming it is to do with the https protocol I’ve tried a few fixes that I found such as:

https://github.com/WordPress/WordPress/blob/master/wp-comments-post.php

but I still have the same problem. Can anyone help.