It has come to our attention that iTunes has changed the display of show pages inside the iTunes store. They now show 20 episodes in the episode list on the show page, whereas they previously showed up to 300.
It appears content is still indexed in the search, but the content does not appear in the listing on the show page. This does not affect subscribers, any content in your RSS feed is always available to subscribers.
UPDATE: According to Apple, this is a bug affecting the iTunes desktop clients (not the Podcast apps). The issue is still being investigated. Additional updates will be provided as we are made aware of them.