Got a reply from plugin contributor:
If you are using any cache mechanism at your website and when your website visitors try social login, it just refreshes the webpage without logging them in, you need to exclude the Cookie PHPSESSID from cache.
If you use Varnish, here are the steps to exclude any cookie from cache.
Is Cloudflare using Varnish for cache? how can i exclude the Cookie PHPSESSID from cache?
Thanks