This is also happening on my client sites that I manage. I have not upgraded to this weeks new WordPress Core update yet. The Facebook shares have all disappeared (and they have thousands on each post.) However, the Pinterest shares are still showing. Here is an example https://genevievegerard.com Checkout any recent post (reached via a link on the home page.) They usually have 500-1,000 Facebook shares per week, per post.
The only change we did on the site listed above was update All In One SEO Pack plugin to 2.3.9.1 this week (however, we did deactivate this plugin and the Facebook shares are still missing.)
Does this have anything to do with the recent changes to the Facebook API?
This is a huge problem for clients who have spent years building up their online presence and social proof.
Please address this quickly.