The plugin caches feed output, so there will be a delay between the time a feed is updated and the output of the plugin changes. The documentation doesn't say, but I assume this is by design, to avoid overwhelming RSS feeds with requests for content that probably doesn't change that often.
Kindly refer to the plugin description page which states
Uses fetch_feed, which was introduced in WordPress 2.8. Works and tested in WordPress 3.5. fetch_feed caches feeds for 12 hours. If you want to change the cache time, see http://codex.wordpress.org/Plugin_API/Filter_Reference/wp_feed_cache_transient_lifetime or http://wordpress.org/support/topic/extend-display-limit