多个通知在Android上不起作用

有没有办法解决这个问题?

以下是我的代码:

NotificationManager notificationManager = (NotificationManager)
                                getSystemService(NOTIFICATION_SERVICE);
Intent intent = new Intent(DbInsertService.this, MessageActivity.class);
intent.putExtra("Service",serviceType);
PendingIntent pIntent = PendingIntent.getActivity(DbInsertService.this, (int) 
   System.currentTimeMillis(), intent,PendingIntent.FLAG_UPDATE_CURRENT);
 Notification n  = new Notification.Builder(DbInsertService.this)
                                .setContentTitle("Message from " +serviceType.getSer_name())
                                .setContentText(messageType.getHis_title())
                                .setSmallIcon(R.drawable.ic_email_variant_grey600_24dp)
                                .setContentIntent(pIntent)
                                .setAutoCancel(true).build();
                        notificationManager.notify(0, n);