I think various factors can contribute to this happening, with one of the major ones being your site's likes going up to fast. Are you doing anything shady on your website (example: providing an incentive to click the like button)? Or is this a perfectly compliant like button on a legitimate site?
I will go with a different angle. Did you do anything to your opengraph? It is easy to mess things up with a slight change to your opengraph.
Edit: And if it is due to opengraph, then you did not lose your likes.