Failed to call didCancel - AVSpeechSynthesizerDelegate

As per apple's document didCancel method will be called after stopSpeaking(at:) method call, instead didFinish method is being called.

But in reality, so far I've checked: it's working perfectly on iOS 13.2.2, but after iOS 15. Is there anything I'm missing to configure. But it did work perfectly without doing anything on previous version.