Dear Nicholas,
hope this message finds you well. I am not sure if this is a bug or not. However on the lastest Admin Tools and latest J2.5.8
the option SEO Tools (Convert all links to HTTPS when site is accessed over SSL)
works!And I love it.
But I found, that it also converted on my site all EXTERNAL links to EXTERNAL domains. Needless to say, if they do not have a certificate it creates an error.
Not sure if this is my site only, however I thought I let you know,
thank you,
Matthias