I just purchased a 2018 GMC Terrain and the same thing is happening with my touchscreen. It’s very infrequent, maybe once every two weeks but frustrating. I needed to use the Apple CarPlay in order to have the Maps appear on the car monitor but couldn’t get the touch screen to respond. I couldn’t even get the radio to play. I kept plugging my phone in and out using the USB port and suddenly, the touch screen started working. Very frustrating.