Old episodes are missing
AntennaPod is a decentralized podcast app. This basically means that there is no central server that knows everything about each podcast.
Episode information is therefore taken directly from the publisher’s website. When you are subscribed to a podcast, AntennaPod copies and stores information about each new episode in the app. This information is kept even if it is no longer available on the publisher’s site.
Many publishers only keep online (information about) the most recent episodes. So when you just subscribed to a podcast, your AntennaPod installation doesn’t have access to information about the older episodes. To get all past episodes listed in the app, you can contact the podcaster and ask them to (reach out to their hoster to) support ‘paged feeds’ (technical information).