Firstly, congrats on the plugin, it really is excellent and thank you for continually providing support and development, you're a credit to the plugin community.
I've been having similar issues with the facebook counter for months now.
I've found that sometimes (maybe 30%) of the time, the facebook counter displays '0', also it doesn't seem to purge the cache on post 'updates' (does it also purge on Custom Post Type updates/publishes?)?
An example page on my site: http://www.festivalarchive.com/event/iowa-city-jazz-festival-2014/
I was wondering whether it might be possible to add a little check in the plugin to re-check a facebook page likes if == 0, perhaps loop this check 3 times as a failsafe? Then purge cache?
Also maybe a manual purge button in the settings page might be good for testing?
Note I'm using latest plugin version and latest WP version.