Music kept stopping?

My does the same but I can not restart. 

Mine too.  Every long run.  First time was about 90 minutes into a half marathon.  Second time was yesterday about 60 minutes into a treadmill drill.  Yesterday, I continued getting pace change alerts for another 20 minutes or so then those stopped too,  FWIIW, I'm playing a downloaded Amazon Unlimited Playlist over a Trekz Air headset.  I have my 945 set to Smart Notification Off During Activity.  Both times, I was more interested in continuing the activity than messing with my watch but could not get the music to start up again by tapping the headset button that usually starts and pauses the music.

Mine doesn't stop/start it just won't start to begin with since FW 3.9.

Here's what happens to me:

Long press music button.

Connect to headphones.

Then nothing, it sits there on the screen and after waiting 20sec I can try pressing the play button or next button and nothing happens.

I have to exit the app, then go back into amazon music and reselect the current playlist, then the song and album image shows up in the app and play will start.

It used to not be this way before 3.9.

Before I start the activity (running) I start the music (Amazon). After a while, maybe about 20 minutes the music stops playing and I can not start it again. Music screen is then all in gray.