The log you included was the Apache error log, not the PHP one.. so I removed it from the post. The PHP log isn't important given the information you provided.
the URL I gave you first, I actually did get notification of all four comments, but the last one arrived late (something like 24 hours after the comment was made)
This is key. Facebook notifies JFBConnect of the new comment immediately right after it's posted. It's done through Javascript on the page and triggered in the same request after the user hits the "Post Comment" button.
Therefore, if you're not seeing the comment for 24 hours (or however long) after it was posted, it likely means there's an issue with your email server. The emails could be going into a spam box, never being delivered, or something else like that. JFBConnect would not be able to send an email even 2 minutes after the post, so if there's a delay, it's from somewhere else.
What I'd recommend is to add a new email address for the notification of comments/likes. You can add multiple comma-separated emails there, like:
[email protected],[email protected]
Please note, it's comma-separated with no spaces. I'd recommend trying to add some other email address on a different domain (so that the same filters/issues won't affect it) and see if you get more (or quicker) messages at that other email.
I hope that helps narrow things down.. but definitely test and let me know how it goes.
Thanks,
Alex