Galaxy S6 switches MyLink to Bluetooth on alerts

[AC Question]

My phone was factory-reset recently, and since then I've had problems with USB audio to Chevy MyLink (Silverado 15'). Any time I receive a mail message, or lock/unlock my phone, MyLink switches to USB audio. Prior to the factory reset, all functions worked (mostly) as advertised. What would suddenly cause MyLink to switch to USB when the phone alerts? I typically use hands-free calling, and the Pandora app (MyLink via Phone) as well as text messaging features.