Episodes are missing
AntennaPod is a decentralized podcast app. You can find some information about that here. This basically means that there is no central server that knows everything about each podcast. Episodes are loaded directly from the publisher’s website. If the publisher deletes an episode from their website, AntennaPod can no longer access it.
Some publishers support a technique called “paged feeds”. If a publisher supports this, AntennaPod displays all episodes automatically.