I also have the 2.7T and asked at the dealership about this. I was told it activates the defrost mode when using the remote start in extremely cold weather, to assist in not having the windshield fog up when entering the vehicle.
Was having this issue with my 2021 Silverado. Had it at the dealer twice with no resolution. Found this thread and reset my radio. I will see if it holds. If it does I will inform the dealer of the fix.