101st Episode Not Appearing in Podcast App

Episode 101 is not in the feed. It must have been previously or it wouldn't have appeared in the Store; somethow it's been removed since. The Store caches the feeds and visits them periodically, so if the episode isn't restored it will disappear from the Store as well within a day or so.

Apple can't help - it's not they who have caused it. iTunes can only read what's in the feed - it doesn't display episodes with no playable media, but that isn't the case here as the episode isn't in the feed at all. The reason it's in the Store is that, whereas iTunes reads the feed directly, the Store caches feeds, and then visits them in some sort of rotation to check for updates. This is why newly added episodes appear immediately for subscribers but can take a couple of days to appear in the Store.

Similarly, episodes removed from the feed will remain in the Store until it next updates the feed. This is why I estimate that the episode must have been there originally, but then get removed. It couldn't have been Apple who removed it, it has to be something between you and SSP, but I've no way of knowing how this has happened.

If you click on your link above for the feed it will appear formatted for a browser and you will see the episode 101 is missing:

However if you follow the link there to the podcast's website, episode 101 is there. So I would guess that when you add an episode, it appears on the web page, but you have to perform an additional step to get it into the feed.

I can't advise on 'Seriously Simmple Podcasting' which is where the problem lies. Certainly nothing has changed in the feed. With some of these services you have to make an additional step after adding the episode to get it into the feed and this may be the case here.