I’ve had two instances when I was on a what’s app voice call on my iphone walking back to car, got in car and the car has connected to CarPlay during call, after which voice control has failed and upon restarting have been unable to connect carplay. My company iPhone also failed to connect, so not an issue with my personal iPhone. I had to perform a factory reset of the infotainment system and then all was good again, so might be worth trying a factory reset to see if this resolves your issue.