Help with play/pause using Spen

[droidntn]

Yesterday, by pressing the button on the S pen I was able to control the play/pause for playback on Amazon music. But later in the day it stopped working. All of the other gestures work.
Weirdly, the play/pause and all of the air gestures work fine with Pandora.
Any thoughts?
This is a very handy feature that I use when at work and streaming music in my office.