I came across this closed thread:
Having had the same issues, I wanted to let people know of my “solution”/workaround.
Since I usually listen to other streaming platforms like apple music the issue really never occured.
I recently started to listen to my plex library when music stopped playing as soon as the phone locked itself or I locked it by pressing the lock button.
I tried everything the users did concerning battery saving settings as well in the thread above. No improvement.
What did the trick was leaving the plex media player open before locking the screen. The music continued to play.
As soon as I switched apps and the screen locked again, the music would stop playing eventually. After a few seconds only.
So, leave the app open/visible before the screen locks and the music will continue to play.
Hope, this helps.
