WordPress over HTTPS

I have a problem with using my WordPress site over HTTPS. When the certificate is enabled on the domain, it will break some pages. I have noticed the problem is located with meta data loaded with “get_post_meta”. Which to me, makes no sense. On some pages it works as expected, on others not. The function returns false.

I have installed a plugin “WordPress HTTPS” to help me. But without any luck.

I have no idea where to look for a solution, as some pages are working, and some are not. I don’t have a live url at the moment, I’m using a local setup to test this.