MQTTnet.Exception.MqttCommunicationTimeOutException

I met a MqttCommunicationTimeOutException, but I’m not sure what the problem, hope to be able to get help. Version 3.0.5 is used.

This is the exception information：

MQTTnet.Exceptions.MqttCommunicationTimedOutException: Exception of type 'MQTTnet.Exceptions.MqttCommunicationTimedOutException' was thrown.
   at MQTTnet.PacketDispatcher.MqttPacketAwaiter`1.WaitOneAsync(TimeSpan timeout)
   at MQTTnet.Client.MqttClient.SendAndReceiveAsync[TResponsePacket](MqttBasePacket requestPacket, CancellationToken cancellationToken)
   at MQTTnet.Client.MqttClient.PublishAtLeastOnceAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)

This is considered critical code：

MqttClient.UseApplicationMessageReceivedHandler(e =>
{
    MqttClient_ApplicationMessageReceived(e);
});

private void MqttClient_ApplicationMessageReceived(MqttApplicationMessageReceivedEventArgs e)
{
    Console.WriteLine("### 从服务端接收的消息 ###");
    Console.WriteLine($"+ Topic = {e.ApplicationMessage.Topic}");
    Console.WriteLine($"+ Payload = {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}");
    Console.WriteLine();

    // After processing, the theme is republished
    Event_MQTTMessageReceived?.Invoke(e);
}

public void Publish(string topic, string Data)
{
    if (MqttClient != null && MqttClient.IsConnected)
    {
        var _Message = new MqttApplicationMessageBuilder();
        _Message.WithTopic(topic);
        _Message.WithPayload(Data);
        _Message.WithAtMostOnceQoS();
        _Message.WithRetainFlag(false);

        MqttClient.PublishAsync(_Message.Build());

        Console.WriteLine("### 从本地发送的消息 ###");
        Console.WriteLine($"+ Topic = {topic}");
        Console.WriteLine($"+ Payload = {Data}");
        Console.WriteLine();
    }
}