This morning the dealership has checked the car after a night with -20C. The mechanic have seen the problem and is really a problem, it's not the cold protection.
For the moment, oil was added in the transmission (it's the second time the oil level is verified). Probably the first mechanic has not the competence to check the oil level of a transmission, because the first time, the oil level was at maximum!!!!
Crazy. Then again, I've had cars 'grow' brake pads before! That's when you have more thickness than at the previous oil change. And I've concluded that this happens because people check boxes without actually performing the checks.
Glad you got that figured out, man. And I must've lived in SoCal for too long because -10C sounds real cold to me! I don't think I've seen less than 10C in a long time and that is enough to make my TPMS whacky and my tranny sluggish.