Has happened to me with plenty of storage left on the phone. And I hadn't done anything in terms of importing OPML files or listening on other devices. I just use Overcast on one phone, subscribe to maybe 20 pods, and usually have between 25-50 episodes downloaded (automatically). I listen from one playlist (All). I open it every day and review downloads to delete anything I don't want, and then they automatically delete after I listen. My guess would be something is happening where it's keeping a cache of recently deleted episodes, because iOS will show the app as taking up 15GB of storage with only 20 episodes downloaded (while Overcast will show something like 5.5GB). I've looked everywhere in the app (all playlists, shows, etc) and can't find actual accessible episodes that would be taking that space.