Good morning, svh1,
Well, I went to sleep last night realizing that although the principle was right, something wasn’t in the tags I mentioned to you.
I have to go out this morning soon, but will leave you clues, and maybe Ingmar will come in with a more targeted comment.
The HTML tag where you’d expect to find the return URL is <form action=“http://your.url.com/etc.”>.
In EE, this is taken care of in the form tag, as:
{exp:weblog:entry_form weblog="default_site" return="site/index" preview="site/entry"}
the ‘site/index’ in return= is I think equivalent to action= in the HTML form tag.
Why EE is not automatically inserting https:, or simply using relative paths in its construction of the <form action= for you, I am not sure, since you are on an https: access for the page as you say.
What I could suggest is to put a full https://your.site.com/site/entry in the return= parameter of weblog:entry_form. Or similar if you are using some other method in EE.
Hope that gets the point across and helps, and interested what you find that works.
Kind regards,
Clive