'Autoblog' plugin not processing feed

I'm running Autoblog version on a WordPress multisite installation, hosted on WP Engine.

I've set up the plugin to import news from an IP-protected atom feed. This feed only ever contains a single post, which is the news story for that particular day. These are available for import from 8am.

The first post in the feed was processed properly and published as it should. However, since that day, the processing report notice states "There are no new entries in the feed". This is particularly strange because if I test the feed, it reports "I have already imported [title of today's story] so I would have stopped processing".

This suggests that it can see there's a new post, but may already think it's processed it when it hasn't. Could this be because there is only ever one post in the feed that is continually being updated?

Thanks for your help.