Hi laurenbersaglio,
I had the same problem - it came out of nowhere and I just couldn't figure out what was going on. I tried switching off Jetpack's sharing, disabling all my plugins, fiddling with the code, changing themes, but all to no avail. Then as a last resort, someone suggested I try this plugin: http://wordpress.org/plugins/facebook-open-graph-meta-in-wordpress/ and it seems to have sorted things out.
I nearly didn't try it because that particular plugin hasn't been updated in 2 years, plus I couldn't see why in the world it would make any difference, but for me it has worked. I no longer get that Facebook warning message or any others. (After installing, I did have to clear the cache from my site and browser before it kicked in though.)
The plugin does ask you for a Default Image URL but that doesn't make any difference to me, as like you, I use featured images, which override it.
I don't know if this will help you, but good luck.