Async/Await code fails when HttpClient.SendAsync is called, C#

Language: Layout:

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Rextester
{
    public class Program
    {
        static List<Task> runningTasks = new List<Task>();
        
        public static void Main(string[] args)
        {
            int result = 0;

result = HandleCommandLine(args).GetAwaiter().GetResult();
            
            Console.WriteLine("Exiting: " + result.ToString());
        }

static async Task<int> HandleCommandLine(string[] args)
        {
            // headless mode

int result = 1; // true, optimism

result = await HandleControlMode(args).ConfigureAwait(false);

return result;
        }

private static async Task<int> HandleControlMode(string[] Arguments)
        {
            int result = 1; // optimism

try
            {
                List<string> sites = new List<string>() { @"http://localhost/site1", @"http://localhost/site2", @"http://localhost/site3" };
                foreach (string site in sites)
                {
                    Begin(site);    // fire off tasks

// the HandleControlMode method is async because in other circumstances, I do the following:
                    //await Task.Delay(5000); // sleep 5 seconds

}

// wait while all test running threads complete
                try
                {
                    Console.WriteLine("Before Task.WaitAll");                    
                    Task.WaitAll(runningTasks.ToArray());
                    Console.WriteLine("After Task.WaitAll");
                }
                catch (Exception)
                {
                    // not really a catch all handler...
                }
            }
            catch (Exception)
            {
                // not really a catch all handler...
            }

return result;

}

private static void Begin(string site)
        {
            //runningTasks.Add(Task.Factory.StartNew(() => HandlePlayback(runArgs)));
            runningTasks.Add(Task.Factory.StartNew((args) => HandlePlayback((string)((object[])args)[0]), new object[] { site }));
        }

private static async Task<int> HandlePlayback(string site)
        {
            int result = 1;

try
            {
                PlaybackEngine engine = new PlaybackEngine(site);
                bool runResult = await engine.RunCommandLine(site).ConfigureAwait(false);

if (!runResult)
                {
                    result = 0;
                }
            }
            catch (Exception)
            {
                result = 0;
            }

return result;
        }
    }

public class PlaybackEngine
    {
        private static HttpClientHandler ClientHandler = new HttpClientHandler()
        {
            AllowAutoRedirect = false,
            AutomaticDecompression = System.Net.DecompressionMethods.GZip | DecompressionMethods.Deflate
        };
        private static HttpClient Client = new HttpClient(ClientHandler);

public string Target { get; set; }

public PlaybackEngine(string target)
        {
            Target = target;
        }

public async Task<bool> RunCommandLine(string site)
        {
            bool success = true;
            string response = await this.SendRequest().ConfigureAwait(false);
            return success;
        }

private async Task<string> SendRequest()
        {
            string result = string.Empty;

string requestTarget = Target;

HttpMethod method = HttpMethod.Post;
            var message = new HttpRequestMessage(method, requestTarget);

StringContent requestContent = null;
            requestContent = new StringContent("dummycontent", Encoding.UTF8, "application/x-www-form-urlencoded");

message.Content = requestContent;

try
            {
                Console.WriteLine("SendAsync...");
                using (HttpResponseMessage response = await Client.SendAsync(message).ConfigureAwait(false))
                {
                    Console.WriteLine("NEVER REACHED");
                    using (HttpContent responseContent = response.Content)
                    {
                        result = await responseContent.ReadAsStringAsync();
                        System.Diagnostics.Debug.WriteLine(result);
                    }
                }

}
            catch (Exception ex)
            {

}

return result;
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,16 sec, absolute running time: 0,5 sec, cpu time: 0,7 sec, average memory usage: 24 Mb, average nr of threads: 11