I have talked to three different MB service advisors and all said this is a delicate situation. tires buckle in temps under 40, as they are very hard tires, made for performance driving, not winter. was not made aware of this when i bought the car two months ago. tires sound unsafe in this environment.
We have a GLC 43 as well and live in a cold climate. If the temperature has dropped to about 40 you may be experiencing crabbing...check for other links on this site for loads of information. We change to winter tires when the temperature gets close to 40 and the problem goes away. The ride is soooo much better as the summer Continental tires on 21" rims are very firm to say the least. Hope this helps.