Deactivating

Right-click on the pages that are broken and view source. If you see a lot of https links still, that’s your problem.

Since the plugin hasn’t been updated in two years–what with all of the changes to WordPress during that time–I’m guessing there aren’t any functional provisions to remove the “add https” changes from the database and anywhere else they may have been written to while the plugin was activated (e.g., .htaccess files). Additionally, in various cases, plugin developers didn’t necessarily include provisions to remove the code rewrites if their plugin was simply deactivated. It’s often (but not always) the case that such plugins have to be deleted in order to facilitate that process.

Given how long it’s been since the plugin was deactivated, I’d recommend exporting a copy of the database as well as downloading all files in your document root, then performing global searches for the use of https specific to your site (w.g., search for ‘https://mysite.com’ and ‘https://www.mysite.com’). Clean those out (change ‘https’ to ‘http’ in those cases, then overwrite the database with the updated sql file, and replace the files on the server that need updating. But be careful…

Be careful with all htaccess files before making changes–inspect those individually where https was found, and make changes only if you’re sure about what you’re doing (e.g., remove force_ssl, etc.). Also, don’t make changes to https where links point to external sites.

If you’ve gotten this far and don’t understand what I’ve mentioned, you may need to seek the assistance of someone who does.