First of all you are not alone I am having the same problem as well. Its not just the official facebook plugin its going on with the other plugins such as Facebook AWD as well. A quick Google search revealed that its because of the interference of og tags but I am still stuck trying to figure out a way.
I tried the plugin in a fresh installation as well the moderating tool nor the comments are showing up.
And now when I shifted back to my previous Facebook comments plugin, still comments are not showing in moderation tool. I mean I can’t even moderate comments on my website.
This is a really bad plugin from Facebook which have hijacked all the codes and made the website unsocial. Very disappointed.