I believe I know what the trouble may be … … …
I noticed that some of my own pages would often show up as "insecure" when loaded, and since I had two of my own that required inputs, people were reluctant to do this without a working page with lock sign in their browser window.
I therefore had to edit several of my own pages, including some of my includes, such my style sheets, so there were no mixed pages of both some with SSL and some without.
Thus I believe this is the issue, as it is the only possible thing that has changed anywhere. on my site. My style sheet include, for example now says:
<link rel="stylesheet" type="text/css" href="https://xxxxx.com/stylesheets/my_zeroizer.css" media="screen, projection, print, handheld" />
<link rel="stylesheet" type="text/css" href="https://xxxxxx/stylesheets/mainstylesheet.css" media="screen, projection" />
<link rel="stylesheet" type="text/css" href="https://xxxxx/stylesheets/print.css" media="print" />
in order to force the necessary SSL compliance.
With fresh eyes, I am going to investigate further. But since it is the only thing that has changed, I believe that is what it is.
I have already spotted, for example, that the user_registration page has:
$WARegistration = new WA_Include('webassist/plugins/registration/themed/registration.php');
I of course will not and cannot edit any of these, but perhaps you could check?