Hi @Bencherished. I don't have any other music player, so cannot compare on that score.
By "moving the phone", I mean picking it up to wake up the screen; or clicking the power button to wake it up. If I leave the phone alone so that the screen timeout expires, playback will stop for a variable period (a few seconds to some minutes) and then will restart for a few seconds, and then stop again, and so on. Waking up the screen always causes playback to resume immediately, but it then goes intermittent as described after a few seconds of the the screen turning off again.
I don't have any RAM management apps installed.
For now, I force stopped the app and restarted it, and this has resolved the issue again for the time being, but I imagine it will resume again at some point as per this time.
The Wakelock setting was disabled. I've enabled it now and will monitor the effect. Owing to the intermittent nature of the problem, and the fact that playback keeps resuming periodically, I'm guessing that the issue will not be resolved by enabling this, but I'll be happy to be proved wrong.
One factor that may be relevant is that I most frequently use Poweramp through Android Auto. The problem has not occurred at all in this use case. So far it has only occurred when playing through the phone speaker.
Thanks for your help so far.