The plugin redirects based on the current URL the user is at when clicking the login button. It might be that, for some reason, the code could not correctly detect the protocol (https or http) of the current URL and generate an invalid link.
Can you try to add the following piece of code to the file Hybrid/Auth.php from q2a-open-login plugin folder, on line 376?
if( !empty($_SERVER['HTTPS']) ||
See here how that line looks now: https://github.com/alixandru/q2a-open-login/blob/development/Hybrid/Auth.php#L376
Basically you need to add a new condition to that "if" and test again.
If that doesn't work, I will really need the URL of your site to debug. I hope this helps.