I have, like many others, a problem with this plugin to make it work with WPEngine. I've been opening a ticket for this and they told me that WPEngine does not support PHP sessions for their infrastructure. I'm suspecting this would apply also for other WordPress-only optimised hosts which are becoming increasingly popular.
Unfortunately, this plugin relies on PHP sessions (stored on the server) rather than cookies (stored on the user's machine).
However, other "social logins" plugins do work on WPEngine (although they have other quirks or are just simply not as good), and I think it could be perfectly possible to make social connects work without the need of PHP sessions.
Would it be very hard to replace sessions by cookies? From an optimization point of view is also good approach to use server resources (if you have a really busy website where many people connect with social logins this could mean having many sessions used at the same time just for that).
Do you have other ideas? Has someone found a workaround?