Facebook has been making a few changes to site of late. Including a server configuration change that resulted in a wide shutdown of the platform in March.
In addition to this the platform has made some changes to their Ad services.
Facebook has announced it will be removing the Ad Relevance Score on April 30, 2019. The Relevance Score gave advertisers insight into how well the ad may perform on the site and used this as a part of the process to define its reach.