I had this problem. Even though I copied AntennaPod’s data to the external SD card, it did not recognise the files I had collected. I solved it by the following hackery, which requires a rooted phone.
First, note that I moved AntennaPod’s data directory from /storage/emulated/0/Android/data/de.danoeh.antennapod/files to /storage/FB03-5D01/Android/data/de.danoeh.antennapod/files. The problem is that AntennaPod’s internal database stores absolute file paths. However it’s a sqlite database, we we can alter it quite easily.
My phone isn’t rooted, so I couldn’t use the sqlite workflow, but knowing the paths to AntennaPod’s database in built-in memory (/storage/emulated/0/…) and on the SD card (/storage/xxxx-xxxx/…) was hugely helpful. I am non-technical, but know about databases and modifying database tables, so it was very good to know the DB operates.
It turned out for me that deleting and re-downloading was the safest way to go for me.
I want to point out for anyone that comes after me seeking this kind of help that in my case some podcasts had been listened to, so were out of the queue, but the episode’s .mp3 file was still present on the in the built-in memory, because I don’t set AntennaPod to auto-deleted listened-to episodes. (Hence my problem with the huge build-up of files in the built-in memory.)
For those ones, an extra step is necessary. I went to the individual subscriptions and deleted the episodes that were still in the built-in storage, then immediately re-downloaded them. I could observe using SD Maid that the file was removed from the old spot and restored to the new one.
Thanks again for the excellent step by step help. Much appreciated.