Hey ya'll, Let me know if anyone else has experienced this or knows how to 'fix it' 
If I'm busy listening to Apple Music or a YT video on a browser, for some reason if I get a voice note from WhatsApp, and pause anything playing in order to listen to the voicenote - when i have listened to it, and thereafter try resume media via a touch bar play/pause button - it just plays or pauses the voicenote. Then the the play/pause button does not work for Music/Browser YT again until I quit WhatsApp.
It is as if MacOs just automatically decides that WhatsApp's voice note is now the priority / only media for toggling pause/play.