Starting with 3.1 I have been having an issue with external audio source while playing the game on Android. I will frequently listen to a book on tape (audible) while playing the game. This worked great until 3.1. Now it seems that launching gems of war is considered an audio interruption where it was not in the past. So either the audio stops all together or plays at a very low volume.
Same thing is happening to me with spotify. As a workaround I’ve found its possible to multitask out of Gow, pause the audio, multitask back to Gow, then resume the audio playback via the android notification menu (or a smart watch or Bluetooth controls if available).