Hi GermanKiwi,
I resolved this issue using the same solution to "Player not working in IOS". I seems to be a fairly common problem with this plugin, which leads me to believe the developer should really have a page dedicated to it somewhere.
To fix the issue, go back through your "Sermons" and select the already uploaded MP3 file. In the box that comes up, click "File URL", then "Use as location of MP3".
It seems to be the Link URL method that breaks the podcasting feature. Despite my Wordpress installation having "FILE" as the default, I still had to perform the steps above to have the files show up in podcasting. Perhaps the default only applies to image file types?
Hope this works for you.