We’re posting this solution after experiencing problems with the facebook comment box not showing for several weeks causing significant decrees in the user flow to the website.
First off the problem is not with the plugin. It is a great plugin with one fault – it deals with facebook content and facebook just cannot get it right sometimes.
WHAT to DO?
Check all your other plugins for conflict, especially:
1. Plugins that load j-query simultaneously or in a lazy load regime
2. Plugins that use iFrame to load content
3. And most of all, plugins that load more content from facebook, especially the ones implementing the new like/share facebook button.
In our case a social sharing plugin Digg-Digg, which is kind of an eye-candy when you start using it was crashing the facebook comment box, which generally loads last at the end of the page.
Digg-digg and other social media plugins worked well with SEO facebook comments until recently when facebook started changing (yet again) their protocols. In our case the newly implemented Share button by facebook used by Digg-digg was crashing the comment box sporadically. As a result facebook comments were not showing under every post in Chrome and FireFox and sometimes even IE. You had to reload several times before seeing the box and even then it was not guaranteed. Digg-digg also uses the iFrame for one of their floating button styles (which is absolutely incompatible with any mobile browser).
As a solution, we replaced Digg-Digg with Really simple Facebook Twitter share buttons, which now has other social media buttons as well. It did the trick and does the same thing for social sharing as other more fancy plugins.
So again – SEO facebook comments plugin works well and is tested up to WP 3.8 in our case. But make sure you do not have any of the above conflicting with it. Hats off to the developer(s).