SteamMasterServer.ServerQuery() not calling back SteamMasterServer.QueryCallback callback.

SteamServerScraper.cs

using System;
using SteamKit2;


namespace SteamServerScraper
{
    class DebugLogListener : IDebugListener
    {
        public void WriteLine(string category, string msg)
        {
            String timestamp = DateTime.Now.ToString("MM/dd/yyyy HH:mm:ss.fffffff ");
            Console.WriteLine("DebugLogListener[{2}] - {0}: {1}", category, msg, timestamp);
        }
    }

    class Program
    {
        private static SteamClient steamClient;
        private static SteamUser steamUser;
        private static SteamMasterServer steamMasterServer;

        private static CallbackManager callbackManager;

        private static bool isRunning;

        private const uint RustAppId = 252490;

        static void Main(string[] args)
        {
            DebugLog.AddListener(new DebugLogListener());
            DebugLog.Enabled = true;

            steamClient = new SteamClient();

            callbackManager = new CallbackManager(steamClient);

            steamUser = steamClient.GetHandler<SteamUser>();
            steamMasterServer = steamClient.GetHandler<SteamMasterServer>();

            callbackManager.Subscribe<SteamClient.ConnectedCallback>(OnConnected);
            callbackManager.Subscribe<SteamClient.DisconnectedCallback>(OnDisconnected);

            callbackManager.Subscribe<SteamUser.LoggedOnCallback>(OnLoggedOn);
            callbackManager.Subscribe<SteamUser.LoggedOffCallback>(OnLoggedOff);

            // Subscribe to SteamMasterServer.ServerQuery callback
            callbackManager.Subscribe<SteamMasterServer.QueryCallback>(OnMasterServerQueryCallback);

            isRunning = true;

            Console.WriteLine("Connecting to Steam...");

            steamClient.Connect();

            while (isRunning)
            {
                callbackManager.RunWaitCallbacks();
            }
        }

        private static void OnMasterServerQueryCallback(SteamMasterServer.QueryCallback queryCallback)
        {
            // Print out server addresses
            foreach (var server in queryCallback.Servers)
            {
                Console.WriteLine(server.EndPoint.Address);
            }
        }

        private static void OnConnected(SteamClient.ConnectedCallback connectedCallback)
        {
            Console.WriteLine("Connected to Steam! Logging in anonymously");

            steamUser.LogOnAnonymous();
        }

        private static void OnDisconnected(SteamClient.DisconnectedCallback disconnectedCallback)
        {
            Console.WriteLine("Disconnected from Steam");

            isRunning = false;
        }

        private static void OnLoggedOn(SteamUser.LoggedOnCallback loggedOnCallback)
        {
            Console.WriteLine("Successfully logged on anonymously!");

            // When logged in start ServerQuery
            steamMasterServer.ServerQuery(RustServerQueryDetails());

            Console.WriteLine("Querying Steam Master Server...");
        }

        private static void OnLoggedOff(SteamUser.LoggedOffCallback loggedOffCallback)
        {
            Console.WriteLine("Logged off of Steam: {0}", loggedOffCallback.Result);
        }

        static SteamMasterServer.QueryDetails RustServerQueryDetails()
        {
            return new SteamMasterServer.QueryDetails
            {
                Region = ERegionCode.World,
                AppID = RustAppId,
                MaxServers = 10000
            };
        }
    }
}