It may be this is due to changes Facebook is making, see this post. Hopefully they implement their changes quickly
https://developers.facebook.com/blog/post/2018/04/04/facebook-api-platform-product-changes/
I have the same problem. Plugin worked great for ages, but in last few days events have stopped showing. Is there any chance of a fix? This was a great plugin.
If it helps the site is online at http://www.solidarity.asn.au, you can see the two comments widgets on the right sidebar on homepage.
