std::async with std::future_status::timeout, times out every alternate time on iOS only

I am using an std::async in the C++ part of my app to do a heavy transaction which has chances of taking a very long time in case of something wrong with the network. So I use an std::async combined with std::future waiting for a time out set which saves me from getting hung up when the transaction takes very very long. It gets called every time the user clicks a certain button on UI.

This C++ code of mine gets used on 4 different platforms, namely iOS, Android, OSX & Windows. Following is way I use std::async to do this heavy operation.

//Do the operation in async
std::future<size_t> my_future_result(std::async(std::launch::async, [this]() {
  size_t result = someHeavyFunctionCall();
  return result;
}));

//try to get the status of the operation after a time_out
std::future_status my_future_status = my_future_result.wait_for(std::chrono::milliseconds(some_time_out));
if (my_future_status == std::future_status::timeout) {
  std::cout << "it times out every alternate time on ios only" << std::endl;
}
else if (my_future_status == std::future_status::ready) {
  if (my_future_result.get() > 0)
      //we are all fine
}

Above std::async & std::future_status technique works fine on all platforms. Its only on iOS, I get a problem where the future times out every alternate time the user clicks the button.

Is there something I should correct upon the way I am using std::async & std::future_status ? What might be wrong ? I have tried to search this a lot. I don't get anything other that the information that std::async is not ready for all platforms. Am I hitting a problem that std::async has on iOS ?

I am new to this kind of async+futures based C++ programming. Do, let me know if I am doing an obvious mistake here