SSL Insecure Content Fixer v2.1.2 has just been released. This release fixes detection of HTTPS on 123-reg sites and others using
WordPress has trouble detecting HTTPS in some hosting environments, and 123-reg sites commonly run into this problem. Many common “fixes” for this just don’t work in that environment.
From working through a recent support request, it appears that 123-reg does in fact provide a clue when a page has been loaded on HTTPS. It sets the environment variable
HTTP_X_FORWARDED_SSL to “1” when the page was loaded on HTTPS, which is unfortunately different to other hosts who use that environment variable and set it to “on”.
SSL Insecure Content Fixer now handles both values, so WordPress websites hosted with 123-reg can now easily enable HTTPS. The settings page will now recommend
HTTP_X_FORWARDED_SSL for the HTTPS Detection method, on correctly configured websites.
You can update to version 2.1.2 from your WordPress plugin admin page. Here’s the full changelog for SSL Insecure Content Fixer.