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.
I installed sqlite in Termux:
pkg install sqlite
I stopped AntennaPod. Actually, I froze it using Titanium Backup and backed up its data, just in case.
Then I opened AntennaPod’s database:
sudo sqlite3 /data/data/de.danoeh.antennapod/databases/Antennapod.db
Then I updated the paths like this:
update FeedMedia set file_url = '/storage/FB03-5D01' || substr(file_url, length('/storage/emulated/0/')) where file_url glob '/storage/emulated/0/*';
Then closed the database:
After that, I unfroze AntennaPod and launched it and it knew about all the downloads I had collected.
This won’t solve the problem for everyone, but if you’ve got a rooted phone and are comfortable with the command line it might help you.