Native C++ unit test in VisualStudio crashes when using multiple threads with thread local storage

I try to write unit tests or my Visual C++ Win64 native static library. I'm using VC++ 2017.

The tests fail, when I create additional threads in my test and use complex thread_local variables, like in this example:

In my lib:

    #include <unordered_map>
    #include<string>

    class TlsObject
    {
    public:
        static void clear_map() {
            mymap.clear();
        }

    private:
        thread_local static std::unordered_map<std::string, std::string> mymap;
    };

    ...

    thread_local std::unordered_map<std::string, std::string> TlsObject::mymap;

Here is the unit test code:

    #include "stdafx.h"
    #include "CppUnitTest.h"
    #include "../TLSUnittest/TlsObject.h"
    #include <future>
    #include <string>
    #include <unordered_map>

    using namespace Microsoft::VisualStudio::CppUnitTestFramework;

    namespace SomeUnittest
    {       
        TEST_CLASS(UnitTest1)
        {
        public:
            TEST_METHOD(TestMethod1) {
                TlsObject::clear_map(); // works fine here!!
                auto future = std::async(std::launch::async, []() { 
                    TlsObject::clear_map(); // throws exception here!!
                    return 0; });
                future.wait();
            }

        };
    }

It seems as if the constructor of the std::unordered_map was not called before entering the lamda code. Therefore my code produces a segmentation fault. This finally causes the unit test to fail.

The same code as in the unit test works fine when I link it to a console .exe.

What could be the reason for the unit test failing, while the .exe has no problem?