CThreadPoolX::~CThreadPoolX()
{
    terminated = true;
    jobCV.notify_one();
    thread.join();
}

EP>* Каждый рабочий поток делает в цикле try_pop из очереди очередей клиентов. Если получилось достать очередь клиента — то делаем try_pop задания из его очереди, если задание есть — то выполняем его, потом очередь клиента ставится (push) в конец общей очереди.

S>CThreadPoolX::~CThreadPoolX()
S>{
S>    terminated = true;
S>    jobCV.notify_one();
S>    thread.join();
S>}
S>

CThreadPoolX::~CThreadPoolX()
{
}

void CWorkThread::ThreadFunc()
{
    std::unique_lock<std::mutex> lock(mutex);

    while (!this->terminated)
    {
        while (!this->task)
          cv.wait(lock);

        std::lock_guard<std::mutex> lockWorkFlag(busyFlag);

        try
        {
            std::cout << "Started  Client " + std::to_string(clientID)+" in workerThread " + std::to_string((int)this) + "\r\n";
            if (this->task)
                this->task->Execute();
        }
        catch (const std::exception &e)
        {
            //Log
        }

        this->task = nullptr;

        std::cout << "Finished Client " + std::to_string(clientID) + " in workerThread " + std::to_string((int)this) + "\r\n";

        clientTaskFinisher->FinishClientTask(clientID);
    }
}

void CWorkThread::RunTask
    this->task = task; // #1

void CWorkThread::ThreadFunc
        while (!this->task) // #2
              cv.wait(lock);

Two expression evaluations conflict if one of them modifies a memory location (1.7) and the other one accesses or modifies the same memory location.
...
The execution of a program contains a data race if it contains two conflicting actions in different threads, at least one of which is not atomic, and neither happens before the other. Any such data race results in undefined behavior.

    while (!this->task) // <--- under this->mutex
        cv.wait(lock);

    std::lock_guard<std::mutex> lockWorkFlag(busyFlag);
    this->task = task; // <--- under this->busyFlag

void CWorkThread::RunTask(int clientID, CTask* task)
{
    this->task = task;
    this->clientID = clientID;

    cv.notify_one();
}