Persistent Session and Queuing Messages java to android

HiveMQ Cloud
1

Hello, I hope you are doing well.
Firstly I wanna give a small background about us. We are a media & tech company which we have over 6,000 IoT devices around the world and we keep growing. And we are planning to use hivemq cloud for our device communications.

I have a question / problem about Persistent Session and Queuing Messages.
Here is the scenario:
I have a publisher (java server) which is publish message and I have a receiver (android client). When android client it online it gets the messages which amazing, working very well.
However, when I kill the android app and keep sending message from server and when I open android app, android does not receive previous messages.

Server side:

final Mqtt5BlockingClient client = MqttClient.builder()
        .useMqttVersion5()
        .serverHost(host)
        .serverPort(8883)
        .sslWithDefaultConfig()
        .buildBlocking();

    // connect to HiveMQ Cloud with TLS and username/pw
    client.connectWith()
            .simpleAuth()
            .username(username)
            .password(UTF_8.encode(password))
            .applySimpleAuth()
            .noSessionExpiry()
            .cleanStart(false)
            .send();

    // This code is running every 15 sec
    String now = LocalDateTime.now().toString();
    String message = String.format("Hello: %s", now);
    // publish a message to the topic "my/test/topic"
    client.publishWith()
            .topic("hasan-device/sayHello")
            .payload(UTF_8.encode(message))
            .retain(true)
            .qos(MqttQos.AT_LEAST_ONCE)
            .noMessageExpiry()
            .send();

Client side:

    // create an MQTT client
    final Mqtt5BlockingClient client = MqttClient.builder()
            .identifier("my-device-1")
            .useMqttVersion5()
            .serverHost(host)
            .serverPort(8883)
            .sslWithDefaultConfig()
            .automaticReconnectWithDefaultConfig()
            .buildBlocking();

    // connect to HiveMQ Cloud with TLS and username/pw
    client.connectWith()
            .simpleAuth()
            .username(username)
            .password(UTF_8.encode(password))
            .applySimpleAuth()
            .noSessionExpiry()
            .cleanStart(false)
            .send();

    // subscribe to the topic "my/test/topic"
    client.subscribeWith()
            .topicFilter("hasan-device/sayHello")
            .retainHandling(Mqtt5RetainHandling.SEND)
            .send();

    // set a callback that is called when a message is received (using the async API style)
    client.toAsync().publishes(ALL, publish -> {
        byte[] message = publish.getPayloadAsBytes();
        LOGGER.info("Received message: {} -> {}, ", publish.getTopic(), new String(message, UTF_8));
    });