What would cause WatchOS background audio to play ONLY while connected in debug session with XCode and fail otherwise

Question

I'm using XCode 11.4, WatchOS 6.2, Swift/UI to build a watch app that plays background audio via speaker or BlueTooth pending user choice. Here are the scenarios:

Pass:

1. From XCode run on target watch (series 5)
2. Start audio
3. Screen On: Audio plays via speaker or blueTooth
4. Screen Off (drop wrist): Background audio plays via speaker or blueTooth

Fail:

1. Launch app from watch as user would (not run as XCode target)
2. Start audio
3. Screen On: App plays via speaker or blueTooth
4. Screen Off (drop wrist): Background audio dies for speaker or blueTooth output scenarios

As far as I can tell I've:

1. Set the background capabilities correctly
2. Set Session category and activated prior to playing audio

 do {
                try session.setCategory(AVAudioSession.Category.playback,
                        mode: .default,
                        policy: useBlueTooth ? .longFormAudio : .default,
                        options: [])
                } catch _ {
                    fatalError("AudioSession Failed.")
                }

            session.activate(options: []) { (success, error) in
                guard error == nil else {
                    print("Audio Session Activation Error: \(error!.localizedDescription)")
                    // Handle the error here.
                    return
                }
            }

What might cause this failing behavior when not launched via XCode? Advice on how to debug/fix please. Thanks!