Boost::asio async_connect fails to solve when using "localhost" instead of "127.0.0.1"

I am programming a tcp async client, but it fails to connect when I use "localhost" instead of "127.0.0.1". I mean, 127.0.0.1 works great but localhost fails miserabily. Please, any help fixing it or at least any explanation of what is going on? Maybe I am missusing the tcp::resolver and its results/iterators?

PD: Funny thing is that when using sync version to connect it works with both adresses (I mean using boost::asio::connect(socket, endpoints, error);)

#include <iomanip>
#include <iostream>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

class client
{
public:
    client()
        : io_context(),
          acceptor(io_context),
          socket(io_context)
    {
    }

    void start(const char* host, const char* port)
    {
        tcp::resolver resolver(io_context);
        tcp::resolver::results_type endpoints = resolver.resolve(host, port);//

        socket.async_connect(endpoints->endpoint(), [=](boost::system::error_code error)
        {
            if (!error)
                std::cout << "Connecting to " << host << ":" << port << "\n";
            else
                start(host, port);
        });
    }

    void poll()
    {
        io_context.poll();
    }

private:
    boost::asio::io_context io_context;
    tcp::acceptor acceptor;
    tcp::socket socket;
};


int main(int argc, char* argv[])
{
    if (argc != 1 && argc != 3)
    {
        std::cout << "async.exe <host> <port>" << std::endl;
        return 0;
    }

    const char* host = (argc == 1 ? "localhost" : argv[1]);
    const char* port = (argc == 1 ? "5031" : argv[2]);

    try
    {
        std::cout << "Trying to connect to " << host << ":" << port << "...\n";

        client c;
        c.start(host, port);

        while (true)
        {
            c.poll();
            Sleep(100);
        }
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}

Thank you very much.