Why does socket closing on C# side kill main thread on C++ side?

Question

I have a server side on my raspberry pi written on C++. I have all sockets logic in another thread, so it should not affect to my main thread. Here is the Servers.hpp:

#pragma once

#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <thread>
#include <chrono>

using namespace std;

#define S_OUT_PORT 63253

class TestServer
{
public:
    static void Start();
private:
    static bool threadIsRunning;
    static void LoopOut();
};

Here is the .cpp file:

#include <Servers.hpp>

bool TestServer::threadIsRunning = true;

void TestServer::Start()
{
    threadIsRunning = true;
    thread th(LoopOut);
    th.detach();
}

void TestServer::LoopOut()
{

        try
        {
            int server_fd, new_socket;
            struct sockaddr_in address;
            int opt = 1;
            int addrlen = sizeof(address);

            if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0)
            {
                // logging
                return;
            }

            if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt)))
            {
                // logging
                return;
            }
            address.sin_family = AF_INET;
            address.sin_addr.s_addr = INADDR_ANY;
            address.sin_port = htons(S_OUT_PORT);

            if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0)
            {
                // logging
                return;
            }

            if (listen(server_fd, 3) < 0)
            {
                // logging
                return;
            }

            if ((new_socket = accept(server_fd, (struct sockaddr*)&address, (socklen_t*)&addrlen)) < 0)
            {
                // logging
                return;
            }

            cout << "SC got connection" << endl;

            while (true)
            {
                 //SendString(new_socket, "null:null", 9);
                int strLen = 9;
                string str = "null:null";

                char b[4] = { (strLen & 0xff), ((strLen >> 8) & 0xff), ((strLen >> 16) & 0xff), ((strLen >> 24) & 0xff) };
                const char* p = reinterpret_cast<const char*>(b);
                send(new_socket, p, 4, 0);
                send(new_socket, str.c_str(), strLen, 0);

                this_thread::sleep_for(chrono::milliseconds(20));
            }
        }
        catch (const std::exception& e)
        {
            cout << "SC error" << endl;
        }
    cout << "SC thread exited" << endl;
}

And I start this server just calling TestServer::Start() in main:

int main()
{
    try
    {
        TestServer::Start();

        while (true)
        {
            cout << "Test" << endl;
        
            this_thread::sleep_for(chrono::milliseconds(3000));
        }
    }
    catch (const std::exception& e)
    {
        cout << "Main error" << endl;
    }
    
    return 0;
}

Then when I'm trying to connect to the server from my pc using C# everything is ok. But when I close the socket from C# side, C++ just terminates. Here is how I shut down connection on C# side:

sct.Shutdown(SocketShutdown.Both);
sct.Close();

What could be the reason of this? Why does socket's shutdown and close kill my main thread in C++?
EDIT 1: Here is the output on the server side:

Test
Test
Test
SC got connection
Test
pi@raspberrypi:~/picadCpp/build $ 

And the loop in LoopOut method removed, but result is the same...