He logrado que las notificaciones funcionen en API anteriores, pero no en Oreo. La creación de la notificación hace que mi aplicación siga funcionando bien (sin mensajes en logcat), sin embargo, SystemUI se bloquea y se reinicia en un ciclo sin fin mientras se ejecuta la Actividad. El es el error en logcat para el proceso systemui:

java.lang.IllegalArgumentException: width and height must be > 0

Mi código:

private void showPlayingNotification() {
        NotificationCompat.Builder builder = mNotificationUtils.getAndroidChannelNotification(this, "Play", mMediaSessionCompat);
        if( builder == null ) {
            Log.i("Play Notification","No notification found!");
            return;
        }

        mNotificationUtils.getManager().notify(101,builder.build()); 
}

Inicialicé mNotificationUtils en onCreate del MediaPlayerService que creé.

public class NotificationUtils extends ContextWrapper {

    private NotificationManager mManager;
    public static final String AUDIO_CHANNEL_ID = "com.liftyourheads.dailyreadings.dailyReadingsAudio";
    public static final String AUDIO_CHANNEL_NAME = "Daily Readings Audio Stream";

    public NotificationUtils(Context base) {
        super(base);
        createChannels();
    }

    public void createChannels() {

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            // create android channel
            NotificationChannel dailyReadingsAudioChannel = new NotificationChannel(AUDIO_CHANNEL_ID,
                    AUDIO_CHANNEL_NAME, NotificationManager.IMPORTANCE_HIGH);
            getManager().createNotificationChannel(dailyReadingsAudioChannel);

        }
    }

    public NotificationManager getManager() {
        if (mManager == null) {
            mManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        }
        return mManager;
    }

    public NotificationCompat.Builder getAndroidChannelNotification(Context context, String action, MediaSessionCompat mediaSession) {

        if (action.equals("Play")) {
            return MediaStyleHelper.from(context, mediaSession)
                    .addAction(new NotificationCompat.Action(android.R.drawable.ic_media_pause, "Pause", MediaButtonReceiver.buildMediaButtonPendingIntent(this, PlaybackStateCompat.ACTION_PLAY_PAUSE)))
                    .setStyle(
                            new android.support.v4.media.app.NotificationCompat.MediaStyle()
                                    .setShowActionsInCompactView(0)
                                    .setMediaSession(mediaSession.getSessionToken()))
                    .setSmallIcon(R.mipmap.ic_launcher)
                    .setContentText("Content Text")
                    .setContentTitle("Content Title")
                    .setChannelId(AUDIO_CHANNEL_ID);

        } else if (action.equals("Pause")) {

            return MediaStyleHelper.from(context, mediaSession)
                    .addAction(new NotificationCompat.Action(android.R.drawable.ic_media_play, "Play", MediaButtonReceiver.buildMediaButtonPendingIntent(this, PlaybackStateCompat.ACTION_PLAY_PAUSE)))
                    .setStyle(
                            new android.support.v4.media.app.NotificationCompat.MediaStyle()
                                    .setShowActionsInCompactView(0)
                                    .setMediaSession(mediaSession.getSessionToken()))
                    .setSmallIcon(R.mipmap.ic_launcher)
                    .setContentText("Content Text")
                    .setContentTitle("Content Title")
                    .setChannelId(AUDIO_CHANNEL_ID);

        }

        return null;

    } }