How to stop Speech Recognition Engine when using RecognizeMode.Multiple

Question

I'm using System.Speech within Unity 2018.2 to perform some words check while the player is speaking. Everything is fine, the word recognition is working but I can't stop the SpeechRecognitionEngine.

Here's how I initialize the SpeechRecognitionEngine :

void InitSpeechEngine()
{
    _speechEngine = new SpeechRecognitionEngine();
    Choices fillers = new Choices();
    fillers.Add(FillerWords.ToArray());
    GrammarBuilder gb = new GrammarBuilder();
    gb.Append(fillers);
    gb.Culture = new System.Globalization.CultureInfo("en-US");
    _grammar = new Grammar(gb);

    _speechEngine.LoadGrammarAsync(_grammar);
    _speechEngine.SetInputToDefaultAudioDevice();
    _speechEngine.SpeechRecognized += FillerRecognized;
}

How I start it :

public void StartSpeech()
{
    _speechStarted = true;
    _speechEngine.RecognizeAsync(RecognizeMode.Multiple);
}

And how I try to stop it :

public void StopSpeech()
{
    _speechStarted = false;
    _speechEngine.RecognizeAsyncCancel();
}

So this is not working the error message I have is :

InvalidOperationException: Cannot perform this operation while the recognizer is doing recognition.

What I want to do is monitoring the player speech for certain words and increment a counter when the player says the word. So I need continuous recognition and no push to talk, so the process should be totally invisible for the player. It's working as I want it to work for now, but I can't stop the SpeecehRecognitionEngine...

And I think that due to this error, my Unity editor crashes when I want to start the game again in the editor.

How should I stop the recognition ?