The first recommendation would be to unpair the phone with the car, and to forget all of your Bluetooth devices on the ZenFone AND the car.
Re-pair the car and phone and check for improvement.
If no improvement, back up all of your data and factory reset your phone. Yes I realize this is the nuclear option and can be a pain in the butt. However, since you mentioned that this happened immediately after an update, this is most likely a software issue that can be resolved with a fresh OS environment.
