Usually with WP Super or Total Cache installed, the original wordpress feed is still updating when viewed directly,
but wordpress still serves the old version to Feedburner.
But in your case the original feed has not updated , even when viewed directly.
<!-- Cached page generated by WP-Super-Cache on 2015-10-31 05:41:48 -->
The caching plugin should have an option to disable it only for the feed URLs - which may or may not work.