Based on your question, I assume this is the plugin you are using to enable SSL: WordPress HTTPS.
Considering that the plugin hasn’t been updated in two years and their support questions haven’t been resolved, there may be some compatibility issues with the latest version of WordPress (4.6 at the time of this writing). My recommendation to make sure your website’s URL is running HTTPS everywhere.
THis can be done by executing the following SQL query in your database (phpMyAdmin):
UPDATE wp_options SET option_value = replace(option_value, 'HTTP_URL', 'HTTPS_URL') WHERE option_name="home" OR option_name="siteurl";
UPDATE wp_posts SET guid = replace(guid, 'HTTP_URL','HTTPS_URL');
UPDATE wp_posts SET post_content = replace(post_content, 'HTTP_URL', 'HTTPS_URL');
UPDATE wp_postmeta SET meta_value = replace(meta_value,'HTTP_URL','HTTPS_URL');
Replace the values with the following:
HTTP_URL
> your HTTP link (http://some.site
)HTTPS_URL
your HTTPS link (https://some.site
)
This way, it prevents any mixed-content links from breaking things. I’ve also found a WordPress thread with a similar issue and not sure if you’ve already taken a look at it: