Unreliable CarPlay (iPhone 7, Kenwood DDX6702S)

I'm seeing strange behavior from my iPhone 7 (iOS 11.2.6) when connecting via CarPlay to my Kenwood DDX6702S head unit.

Things I've experienced recently, all seen since iOS 11, none seen with iOS 10:

• Phone disconnects from head unit, leaving display blank, and continuing phone-sourced audio on phone speaker
• Making a phone call by tapping a phone number in some other app goes to the phone call in progress CarPlay screen, then jumps to the head unit's native (bluetooth?) phone call in progress screen
• When a phone call actually connects with CarPlay screen, audio has lots of dropouts and DTMF tones are duplicated or dropped (other end's voice response unit hears them multiple times or not at all)
• Plugging into radio and starting car, the radio thinks carplay is ready but phone is not generating carplay screens, only a blank screen. Unplugging phone from USB connector and reconnecting, or powering off/on radio, usually gets phone to connect again to the radio.

Cellular service is Verizon (US), with VoLTE enabled (LTE voice + data)

Help? Is anybody else seeing this lame behavior? Makes for a dangerously distracting situation when the radio isn't working correctly.