Android: Spotify plays on only 1 channel after a notification

[andreasvio]

When I use a an app while spotify is playing music, e.g facebook, and I get a notification, spotify or android (not sure) does the normal thing of lowering volume to emphasize the notification but when it continues only one of the 2 earpieces is at normal volume level. The 2nd one is either off or very low. I can only recover by killing spotify and restarting it after a while