CarPlay Siri no audio

I have an iPhone XS, iOS 12.2. I have a Mercedes Benz GLC, 2019 (purchased in November 2018), iPhone XS is connected to the GLC with a new Apple lightning cable to the single 'smartphone' USB port (Mercedes does not support CayPlay with Bluetooth).

So, everything seemed to work OK until about a month ago. What happens now, iPhone XS connected, CarPlay is active and displays correctly, if I press the 'voice' button on the steering wheel, the CarPlay display shows the Siri activity screen, but there is no Siri voice. If I get out of Siri, by pressing the GLC Nav button, and then press the voice button again, everything works fine. So, it's like the first activation of Siri doesn't have audio.

The same thing happens with retrieving text messages. Siri will start open the text message screen, the display will show Siri is 'speaking' but there is no audio. If I get out of Messages, and go back into messages, everything works fine.

Very frustrating!

Anyone else seen this behavior???

Thanks!