I'm assuming you use android for this...

This might seem to not make sense, but check the background data usage and the background battery usage.options. Some apps don't take too well if either or both those options are set to disallow. Doesn't make any sense, but it has happened to me on a few apps (for me, most notably Tunein) and it has happened to a friend of mine. On a tablet, there is an audio issue.... on my phone, no issue. On my friend's phone, audio shuts down within a minute of the screen shutting off (assuming that's when the phone locks).