FCM push notification not working on some devices

I can confirm that this implementation works well with One Plus and Xiaomi devices (we have plenty of users using our app from this devices, and no crashes or issues are created from them regarding FCM Notifications).

Cannot confirm anything for Vivo or Oppo (so far, we do know we don't have users using this kind of devices).

The most important thing is that the notification feature is well implemented if regarding the app is either in foreground or background. If someone wants to do a zoom on this matter, this article explains it on a easy way.

Now, the code I use for FCM implementation in Android:

//MyMessagingService

public class MyFirebaseMessagingService extends FirebaseMessagingService {

  public static final String TAG = "Firebase Msg";

  @Override
  public void onMessageReceived(RemoteMessage remoteMessage) {
    Map<String, String> data = remoteMessage.getData();
    final LocalNotification localNotification = new LocalNotification();
    //data --> entityId - entityType - pushNotificationType
    // Check if message contains a data payload.
    if (data.size() > 0) {
        localNotification.setEntityId(data.get("entityId"));
        localNotification.setEntityType(data.get("entityType"));
        localNotification.setPushNotificationType(data.get("pushNotificationType"));
        localNotification.setTitle(data.get("title"));
        localNotification.setBody(data.get("body"));
        localNotification.setIcon(data.get("icon"));
        localNotification.setDate(new Date().getTime());
        localNotification.setRead(false);
    }

    if (localNotification.getEntityId() != null) {
        LocalNotification notificationRetrieved = FirebaseNotificationsHelper.insertLocalNotification(localNotification);
        FirebaseNotificationsHelper.createNotificationInStatus(notificationRetrieved);
    }
  }
}

//Create notification status

static void createNotificationInStatus(LocalNotification localNotification) {

    String notificationChannelId = App.getContext().getString(R.string.default_notification_channel_id);
    String notificationChannelName = App.getContext().getString(R.string.default_notification_channel_name);
    String notificationChannelDescription = App.getContext().getString(R.string.default_notification_channel_description);

    NotificationCompat.Builder notificationBuilder;
    NotificationCompat.Builder notificationBuilderPublicVersion;

    notificationBuilder = new NotificationCompat.Builder(App.getContext(), notificationChannelId);
    notificationBuilderPublicVersion = new NotificationCompat.Builder(App.getContext(), notificationChannelId);

    notificationBuilder.setDefaults(NotificationCompat.DEFAULT_VIBRATE | NotificationCompat.DEFAULT_LIGHTS | NotificationCompat.DEFAULT_SOUND)
            .setWhen(System.currentTimeMillis())
            .setSmallIcon(R.drawable.ic_stat_push_notif)
            .setTicker(localNotification.getTitle())
            .setPriority(NotificationCompat.PRIORITY_HIGH)
            .setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
            .setContentTitle(localNotification.getTitle())
            .setContentText(localNotification.getBody())
            .setStyle(new NotificationCompat.BigTextStyle().bigText(localNotification.getBody()))
            .setPublicVersion(notificationBuilderPublicVersion.setSmallIcon(R.drawable.ic_stat_push_notif).setContentTitle(localNotification.getTitle()).
                    setWhen(System.currentTimeMillis()).setContentText(localNotification.getBody()).build())
            .setGroup(NOTIFICATION_GROUP)
            .setVibrate(new long[]{1000, 1000, 1000, 1000, 1000})
            .setAutoCancel(true);

    int notificationId = SharedPreferencesUtils.getInstance(App.getContext()).getIntValue(PREF_KEY_NOTIFICATION_ID, 0);

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        NotificationManager notificationManager = (NotificationManager) App.getContext().getSystemService(Context.NOTIFICATION_SERVICE);
        NotificationChannel notificationChannel = new NotificationChannel(notificationChannelId, notificationChannelName, NotificationManager.IMPORTANCE_HIGH);
        // Configure the notification channel.
        notificationChannel.setDescription(notificationChannelDescription);
        notificationChannel.enableLights(true);
        notificationChannel.setLightColor(Color.RED);
        notificationChannel.setVibrationPattern(new long[]{0, 1000, 500, 1000});
        notificationChannel.enableVibration(true);
        notificationChannel.setLockscreenVisibility(NotificationCompat.VISIBILITY_PUBLIC);
        notificationChannel.setImportance(NotificationManager.IMPORTANCE_HIGH);
        notificationManager.createNotificationChannel(notificationChannel);
        notificationManager.notify(notificationId, notificationBuilder.build());
    } else {
        /* Kitkat and previous versions don't show notifications using NotificationManagerCompat */
        if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.KITKAT) {
            NotificationManager notificationManager = (NotificationManager) App.getContext().getSystemService(Context.NOTIFICATION_SERVICE);
            notificationManager.notify(notificationId, notificationBuilder.build());
        } else {
            NotificationManagerCompat notificationManager = NotificationManagerCompat.from(App.getContext());
            notificationManager.notify(notificationId, notificationBuilder.build());
        }
    }
    notificationId++;
    SharedPreferencesUtils.getInstance(App.getContext()).setValue(PREF_KEY_NOTIFICATION_ID, notificationId);
}

I donot think that there is a general solution for this since your app is based on google-FCM that means that the android device regularly comunicates with google-internet-services.

As far as i know google-FCM is blocked (= not reachable) in china