As you know, lately, Facebook has done many changes in their privacy policy in order to avoid the leak of their user informations. Facebook has limited the access to certain kinds of content to apps like My Social Book, and as a consequence of these measures, we are no longer able to retrieve some content like comments, tagged posts (if you haven't added them to your timeline), friends post (like birthday posts).

We know this is disconcerting, but it's not a willing from us.

You can ask Facebook to let My Social Book retrieves comments for their customers. If customers complain about that, maybe they will accept it.