Following the media news about Facebook and the ability of “bad actors” to search Facebook based on a telephone number or email address and locate people, Cambridge Analytica and other news where personal data is being used in manner that most people might object to, the system API’s (Application Programming Interfaces) are being reviewed and modified or retired to help to tighten up on security.
If you are using one of two Facebook plugins in your WordPress site, you may find it is no longer working. That is because Facebook have modified the interface. There will be ways around this I expect, but I am going to leave it a few weeks and let the dust settle.
If you find your facebook feed page is corrupted, or at best not looking great because it has a warning message in there, disconnect it from the menu for now.
I understand that there are workarounds, that require admin access to the Facebook Group page and knowledge of a special key and secret. I have not used those when setting up your page. As I find out more I will update this page.
You can read about the changes here if you want to have a go yourself: https://developers.facebook.com/blog/post/2018/04/04/facebook-api-platform-product-changes/