Duplicated messages from Mosquitto server

[ssi-jmandrell]

I have written a small client to receive messages from a Mosquitto server. However, when I use 'mosquitto_pub' to send a single message I receive multiple copies of it in my client. I'd really like to receive only one. Can someone point me to what I'm missing here?

        var mqttFactory = new MqttFactory();

        using var mqttClient = mqttFactory.CreateMqttClient();
        var clientOptionBuilder = new MqttClientOptionsBuilder();
        clientOptionBuilder.WithTcpServer(Config.Url);
        clientOptionBuilder.WithClientId(CoreCommand.Common.Guid.NewGuid());
        clientOptionBuilder.WithCleanSession();
        var mqttClientOptions = clientOptionBuilder.Build();

        // Setup message handling before connecting so that queued messages
        // are also handled properly. When there is no event handler attached all
        // received messages get lost.
        mqttClient.ApplicationMessageReceivedAsync += e =>
        {
            Console.WriteLine($"Received message {Encoding.UTF8.GetString(e.ApplicationMessage.PayloadSegment)}");
            return Task.CompletedTask;
        };

        await mqttClient.ConnectAsync(mqttClientOptions, CancellationToken.None);
        await mqttClient.SubscribeAsync(Config.Topic);

        while (true)
        {
            Thread.Sleep(1000);
        }