Some synthesized text is played with the next synthesized text.

iOS app(Swift) synthesizes sound with MicrosoftCognitiveServicesSpeech-iOS SDK ver.1.15.0. Several sentences are played correctly. The next portion of the synthesized text doesn't play in time. It plays with the next synthesized text.

Result from next code always return SPXResultReason_SynthesizingAudioCompleted:

    DispatchQueue.global(qos: .userInitiated).async { [self] in
        print("SYNTHESIZE: \(text)")
        if let result = try? self.speechSynthesizer?.speakText(text) {
                print("result.reason: \(result.reason.rawValue)")
        }
    }