.NET Core 2
The client just dies instantly when it tries to send a get request to server. If I use Postman then it works fine, but I need to do it via C#. This is the piece of my code which is for getting files from server:
var client = new HttpClient();
client.Timeout = TimeSpan.FromMinutes(timeSpanFromMinutes);
try
{
    // At this code row the application shutdown without any exception. 
    // Even doesn't work the 'catch' block of try\catch...
    HttpResponseMessage response = await client.GetAsync(url + "/Home/Download/" + args[1], 
        HttpCompletionOption.ResponseContentRead);
    // I will not be here    
    Console.WriteLine("Response status code: {0}", response.StatusCode);
    if (response.StatusCode == HttpStatusCode.OK)
    {
        using (MemoryStream ms = new MemoryStream())
        {
            await response.Content.CopyToAsync(ms);
            Console.WriteLine("Data successfully recieved from server. Data length: {0}",
                ms.Length);
            string resultFileName = Path.Combine(resultFolder, new Guid().ToString()
                                                     + resultFileExtension);
            using (FileStream fs = new FileStream(resultFileName, FileMode.Create))
            {
                fs.Read(ms.GetBuffer(), 0, (int) ms.Length);
            }
            Console.WriteLine("The result was saved in the '{0}' file.", resultFileName);
        }
    }
}
catch (Exception ex)
{   // I will not be here
    Console.WriteLine("Exception: {0}", ex.Message);
}
Server is launched and accessible. All variables are initialized and content the valid values. The post request works without problem. I have the problem for get request. I commented the problem code row. 
What can be the reason of such behaviour?
UPD
This is full code of my client side (the problem is for "get" command):
using System;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Reflection;
using System.Threading.Tasks;
using System.Xml.Linq;
namespace Client
{
    class Program
    {
        static void Main(string[] args)
        {
           var task = Task.Run(()=>{
                Work(args);
           });
           task.Wait();
        }
        static async Task Work(string[] args)
        {
            if (args.Length != 2)
            {
                Console.WriteLine("Application invalid parameters.");
                WriteHelp();
                return;
            }
            string xmlFileName = Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location),
                "Client.settings.xml");
            XElement xml = XElement.Load(xmlFileName);
            string url = xml.Element("url").Value?.Trim()?.TrimEnd('/');
            string resultFolder = Environment.ExpandEnvironmentVariables(xml.Element("resultsFolder").Value);
            if (!Directory.Exists(resultFolder))
            {
                Directory.CreateDirectory(resultFolder);
            }
            string resultFileExtension = Environment.ExpandEnvironmentVariables(xml.Element("resultFileExtension").Value);
            int timeSpanFromMinutes = Int32.Parse(xml.Element("TimeSpanFromMinutes").Value);
            switch (args[0])
            {
                // Send data to server
                case "post":
                {
                    string fileName = Environment.ExpandEnvironmentVariables(args[1]);
                    if (!File.Exists(fileName))
                    {
                        Console.WriteLine("File '{0}' not found.", fileName);
                        return;
                    }
                    else
                    {
                        var client = new HttpClient();
                        client.Timeout = TimeSpan.FromMinutes(timeSpanFromMinutes);
                        try
                        {
                            using (FileStream fs = new FileStream(fileName, FileMode.Open))
                            {
                                HttpResponseMessage response = await client.PostAsync(url + "/Home/Upload", 
                                    new StreamContent(fs));
                                Console.WriteLine("Response status code: {0}", response.StatusCode);
                                if (response.StatusCode == HttpStatusCode.OK)
                                {
                                    // The task ID. It is to be used for get the data handling result from server later.
                                    string id = await response.Content.ReadAsStringAsync();
                                    Console.WriteLine("Task ID: {0}", id);
                                }
                            }
                        }
                        catch (Exception ex)
                        {
                            Console.WriteLine("Exception: {0}", ex.Message);
                        }
                    }
                    break;
                }
                // get the result of data handling from server
                case "get":
                {
                    Guid guid = Guid.Empty;
                    if (!Guid.TryParse(args[1], out guid))
                    {
                        Console.WriteLine("Invalid identifier (GUID): '{0}'", args[1]);
                        return;
                    }
                    var client = new HttpClient();
                    client.Timeout = TimeSpan.FromMinutes(timeSpanFromMinutes);
                        try
                        {
                            // TODO: the problem is here
                            var response = await client.GetAsync(url + "/Home/Download/" + args[1], 
                                HttpCompletionOption.ResponseContentRead);
                            Console.WriteLine("Response status code: {0}", response.StatusCode);
                            if (response.StatusCode == HttpStatusCode.OK)
                            {
                                using (MemoryStream ms = new MemoryStream())
                                {
                                    await response.Content.CopyToAsync(ms);
                                    Console.WriteLine("Data successfully recieved from server. Data length: {0}",
                                        ms.Length);
                                    string resultFileName = Path.Combine(resultFolder, new Guid().ToString()
                                                                             + resultFileExtension);
                                    using (FileStream fs = new FileStream(resultFileName, FileMode.Create))
                                    {
                                        fs.Read(ms.GetBuffer(), 0, (int) ms.Length);
                                    }
                                    Console.WriteLine("The result was saved in the '{0}' file.", resultFileName);
                                }
                            }
                        }
                        catch (Exception ex)
                        {
                            Console.WriteLine("Exception: {0}", ex.Message);
                        }
                    break;
                }
                default:
                {
                    Console.WriteLine("Unknown command: {0}", args[0]);
                    WriteHelp();
                    return;
                }
            } 
        }
        private static void WriteHelp()
        {
            string text =
@"
Client.dll
(c) Andrey Bushman, 2018
This client allows to send data to server and get the results of their handling.
The application using format:
    dotnet Client.dll <command> <parameter>
## COMMAND
    post - send file to server. The request contains status code and GUID for getting the data handling result later.
    get - get data handling result by GUID. If result doesn't exist still then recuest code is 'File not found'. 
## PARAMETER
    It is the file full name for the 'post' command or the GUID for the 'get' command.
## EXAMPLES
Upload the file to server:
    dotnet Client.dll post /home/andrey/tmp/data.foo
Download the data handling result from server by GUID:
    dotnet Client.dll get 3d600895-f11c-4fa0-865e-411d52daf469";
            Console.WriteLine(text);
        }
    }
}
Full code sources are here on GitHub.