Thanks for confirming the status on Feedly and w3c validator. Alas, the only plugins I have on my WP installation are:
Secondary Title,
Related Posts for WordPress,
WordPress Facebook Post Comments,
TablePress,
Multiple Post Thumbnails,
Caption Linker, and
WP Social Avatar
None of these look like they could have anything to do with security or RSS feeds. As for the server, I am using Bluehost and they have thousands of other WP bloggers hosted on their servers; I wonder why they would block something as inconspicuous as RSS!?