I started getting a "Failed to play file" warning a while back, and tried several things to fix it:
Check storage permissions
Check the app wasn't being put to sleep
Re-install, restart phone, check for updates, etc.
None of these things worked, so I dug around a bit and found that the Decoder listed under "Settings > Audio > Audio Info" was "?", and I imagine that is the problem (picture attached). I think it started happening after an Android update, but I'm not 100% sure.
Info:
Poweramp Build - build-967-bundle-play
Samsung Galaxy S20 FE 5G
Android 13/One UI 5.1, updated June 1, 2023
Stock ROM
Steps to reproduce - unknown
I have "Send Errors to Developer" enabled, and I just did the "Settings > Support > Send Log" email as well in case that helps.