Despite having the 'add opengraph meta data' box unchecked on this page of the settings: wp-admin/admin.php?page=wpseo_social,
Meta data still appears.
This is causing a conflict with the facebook social publisher plugin which also has facebook meta data. So, the OG meta data appears twice in each post. This gives the error: More Than One OG URL Specified: in the Facebook Dev URL tester (https://developers.facebook.com/tools/debug)
This is a bug in WordPress SEO.
I previously had the 'add opengraph meta data' box checked, so perhaps it's not getting reset properly when it's unchecked.