I dont no about the plugin, but the default on feed-function of WordPress have a cache, there cache all content for 12 hour and then regenerate the content.
You can change this via a small function, like in a plugin or you copy the source to the functions.php
of the current active theme; but a plugin is better for maintenance and control your install.
add_filter( 'wp_feed_cache_transient_lifetime', create_function( '$a', 'return 1800;' ) );
You can change the cache time. In this example the 1800 seconds.
It is also possible to deacivate the cache. I doing this on my development install.
function do_not_cache_feeds(&$feed) {
$feed->enable_cache(false);
}
if ( defined('WP_DEBUG') && WP_DEBUG )
add_action( 'wp_feed_options', 'do_not_cache_feeds' );
See also this Link to more background information