How to prevent notification icon in shade from disappearing when put application in background

Question

In my android app I am using notification service (NotificationManagerCompat). My problem is when I get more then one notification, I see them in the shade, but when I put my application in the background, all the notifications in the shade disappear. How do I prevent them from disappearing, and keep them in the shade while my app is moving from the foreground to the background?

Here is my code example:

Intent pushHanlderActivityIntent = new Intent(this, PushHandlerActivity.class);
        pushHanlderActivityIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        pushHanlderActivityIntent.putExtra(PUSH_BUNDLE, extras);
        pushHanlderActivityIntent.putExtra(START_IN_BACKGROUND, true);

        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, pushHanlderActivityIntent, 0);

        NotificationCompat.Builder builder = new NotificationCompat.Builder(getApplicationContext(), CHANNEL_1_ID)
                .setSmallIcon(R.drawable.clalit_notification) 
                .setContentTitle(title)
                .setContentText(message)
                .setContentIntent(pendingIntent)
                .setAutoCancel(true)
                .setPriority(NotificationCompat.PRIORITY_DEFAULT);

        NotificationManagerCompat notificationManager1 = NotificationManagerCompat.from(getApplicationContext());
        //show the notification in shade
        int random = (int)(Math.random() * 50 + 1);

        notificationManager1.notify(random,builder.build());