I've just upgraded to Android 11 59.1.A.2.96 on an Xperia 10II. I've used Poweramp for a few years, now on build 905.
I noticed the sound pausing using BT or headphones. Tried a variety of settings then spotted as the display dims the handset locks and audio stops. Turns out I had given permission to Nova Launcher to control the screen lock through - Settings / Security / Device Admin Apps'.
Hope this helps someone.