Why conditional_variable::notify_all may not wake up any thread?

I use conditional_variable::notify_all() to wake up a waiting thread(only one thread is waiting for the unique_lock indeed).

This code snippet works well at most time, but the log files(for details, see below) indicates that the parent thread could not aquire the unique_lock after the new created thread allready returned.

I would be grateful to have some help with this question.

Here is the related code snippet:

void MainWindow::deployAction(void)
{
    std::condition_variable cvRunOver;
    std::mutex mtxRunOver;
    std::unique_lock <std::mutex> ulkRunOver(mtxRunOver);
    QString workerThreadRes;
    std::thread workThread([&]()
    {
        workThread.detach();

        do_some_process_for_seconds();
        
        cvRunOver.notify_all();
        LOG(INFO)<<"to leave the subthread";
        google::FlushLogFiles(google::GLOG_INFO);
        return;
    });

    while (cvRunOver.wait_for(ulkRunOver, std::chrono::milliseconds(100)) == std::cv_status::timeout)
    {
        qApp->processEvents();
        auto curTim = std::chrono::steady_clock::now();
        std::chrono::duration<float> escapedTim= curTim-lastTim;
        if(std::chrono::duration_cast<std::chrono::seconds>(escapedTim).count()>=5)
        {
            LOG(INFO) << "processEvents()";
            google::FlushLogFiles(google::GLOG_INFO);
            lastTim = curTim;
        }
    }
    
    LOG(INFO) << "get lock and continue to run";
    google::FlushLogFiles(google::GLOG_INFO);
}

Here is the related log when the program does not work as experted:

Log line format: [IWEF]hh:mm:ss.uuuuuu threadid file:line] msg
20:19:14.638686 272568 mainwindow.cpp:208] to leave the subthread
20:19:17.669246 10256 mainwindow.cpp:221] processEvents()
20:19:22.678846 10256 mainwindow.cpp:221] processEvents()
20:19:17.669246 10256 mainwindow.cpp:221] processEvents()
20:19:22.678846 10256 mainwindow.cpp:221] processEvents()
20:19:17.669246 10256 mainwindow.cpp:221] processEvents()
20:19:22.678846 10256 mainwindow.cpp:221] processEvents()
20:19:17.669246 10256 mainwindow.cpp:221] processEvents()
...