CarPlay defaults to Phone Call

Whenever I connect my iPhone 12 ProMax to wired Car Play, I get no audio from the car or iPhone. When I try to adjust the volume, the car’s display says “adjusting phone volume” even though no phone call is active. So apparently CarPlay thinks that there is an active call even though there is none. I have to restart the iPhone while connected to CarPlay; then it works as expected. But the next time I reconnect to CarPlay, the same thing happens. I have to restart the phone every time. It worked fine until yesterday, when this started happening.