This simple multithreading C++ may sometimes crash (SIGSEGV) or remain blocked forever inside waitStart. Can you figure out why?

problematic_miltithreading.cpp

#include <iostream>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <atomic>

// The purpose of the this apparently fine application is to make you appreciate thread santizers
// https://clang.llvm.org/docs/ThreadSanitizer.html

class Foo{

public:
    Foo(): _start_requested(false), _stop_requested(false), _thread( &Foo::loop, this )
    {}

    void loop()
    {
        while(!_stop_requested)
        {
            waitStart();
            std::cout << "loop" << std::endl;
            std::this_thread::sleep_for( std::chrono::milliseconds(200) );
        }
    }

    void waitStart()
    {
        std::unique_lock<std::mutex> lock(_mutex);
        while( !_start_requested )
        {
            _start_signaler.wait(lock);
        }
    }

    void startLoop()
    {
        std::unique_lock<std::mutex> lock(_mutex);
        _start_requested = true;
        _start_signaler.notify_all();
    }

    void stopLoop()
    {
        _stop_requested = true;
        _thread.join();
    }

private:
    std::atomic_bool _start_requested;
    std::atomic_bool _stop_requested;
    std::thread _thread;
    std::mutex _mutex;
    std::condition_variable _start_signaler;
};

int main()
{
    Foo foo;
    foo.startLoop();
    std::this_thread::sleep_for( std::chrono::seconds(1) );
    foo.stopLoop();
    return 0;
}