All podcast reviews/ratings have disappeared

It can't be a feed issue since they are completely independent of the feed. It's probably another interesting glitch in the Store to add to the 'missing episodes' one. You could try querying it with Support, if for no other reason than to make sure they know it's going on. Goto https://itunespartner.apple.com/en/podcasts/overview and click the 'Contact Us' link at the bottom of the page.