I found solution, in facebook-comments-sync/fbcs-frontend.php file:
Previous
js.src = "//connect.facebook.net/<?php echo $options['language']; ?>/sdk.js#xfbml=1&version=v2.4&appID=<?php echo $options['app_ID']; ?>";
Change to
js.src = "//connect.facebook.net/<?php echo $options['language']; ?>/sdk.js#xfbml=1&version=v2.4&appId=<?php echo $options['app_ID']; ?>";
only change variable appID to appId
and its working properly.