Hmm, I know we do have a few issues with the current triggers to rebuild cache and rss feeds as they aren't extremely reliable on their runtime on all setups. That's the main reason we're redoing our scheduler v8.
What you can do for now, is if you have the ability to run cron jobs and can run PHP from the command line, you could setup a cron to run a script like the below every 10 minutes or so to have it manually rebuild the rss, just like hitting the clear cache button in the control panel (which you said works). Cron job would be something like:
*/10 * * * * php /path/to/the/script/below
<?php
chdir("/path/to/libs");
require("admin.inc.php");
generate_rss_feeds(1);
?>
