Hi Mark, thanks for the quick response.
* I only updated the WP core and the WP RSS Aggregator plugin. Just to be sure I’ve now deactivated all of the plugins apart from WP RSS Aggregator, but the problem persists.
* I’ve not made any changes to the feed sources, settings or shortcodes on the staging site.
* I was using the Excerpts and Thumbnails add-on (which you can see working in the ‘article of the month’ feed on the live site), but it’s currently deactivated on the staging site.
Thanks,
Tim