Running an std::async in a loop. Consistent results

I am trying to parallelize calculations and writing the results in order to a vector. I'm using an std::async. The program works perfectly with a short pause (commented line). Without this pause, the program crashes.

Code:

class AsyncDispatcher {
 public:
  /* Data is a custom class with data that contains a ID.
   * The object contains no
   * links or pointers.*/
  vector<Data> calcResult(vector<Params> params) {
    vector<Data> result;
    vector<std::future<NumberedData>> futures;

    threadID = 0;
    for (auto param : params) {
      futures.push_back(((std::async(std::launch::async, [&]() {
        this_thread::sleep_for(chrono::milliseconds(100));  // not workable without this command 
         //^^^^^^^^^^^^^^^^^^^^^^^^^
        return NumberedData(filler.createData(param, threadID), threadID);
      }))));
      threadID++;
    }

    for (auto& f : futures) {
      result.push_back(f.get().data);
    }
    return result;
  }

  AsyncDispatcher() : threadID(0) {}

 private:
  int threadID;
  Filler filler;//fills an Data with numbers
};

Thanks for any advice. And I'm sorry.