Hello Harvey,
The below is just a suggestion, but as you can tell it's frustrating to test issues on a live site without negatively impacting users.
Create a "test" forum and restore a backup of your "live" forum into it.
1. Create a new CName record and Enable https on the test forum
2. Ensure that all of your test forum embedded links have "https://" instead of the relative path.
3. Allow the forum to be viewed without embedding (basically disabled the forced nabble re-direct). I know it's ugly when users
"break out" of the iframe but it helps in testing.
4. Allow, your site visitors (if possible) to view your site *both* with or without https and no forced re-directs. Example:
5. Disable any scripts that force URL redirection on the forum links.
Basically what you will be looking for (both with and without embedding) and making a note of is:
- Forum links that don't default to https
- Mixed content errors (this will be obvious if your site is visited via "http" only)
- Loading and display errors / issues.
- Poke around to see what works and what doesn't.
The main goal would be to find out if the issue is with the embedding or something else. Without making changes to your main site and thus affecting users.
My own testing reveals that images are not getting updated to use "https" and this causes the mixed content error with or without embedding.
I also found links that display "http" however, when clicked they actual go to the "https" location.