I also tried deactivating then reactivating the plugin and re-saving permalinks but no joy.
I also had permalinks set to ‘Post Name’.
Nothing in the apache error.log
What I found is that the Plain link format for the podcast feed – e.g. https://worstcasescenario.ie/?feed=podcast – works even if Permalinks are set to “Post Name”.
As a temporary workaround I have just resubmitted the Plain link format for the feed to iTunes. That keeps our links working correctly, and ensures that iTunes has a valid feed.