Good morning and welcome to the forum!
What's probably going to need to happen is that your car is going to need to sit at the shop overnight when you know it's going to be cold enough to duplicate the problem.
I can ask a guy at work, but what I suspect it happening is that the lower motor mount is hydraulic (fluid filled) and the oil inside of it has solidified when it's that cold. But I'll need to verify that they are hydraulic before I can say for sure.
What's probably going to need to happen is that your car is going to need to sit at the shop overnight when you know it's going to be cold enough to duplicate the problem.
I can ask a guy at work, but what I suspect it happening is that the lower motor mount is hydraulic (fluid filled) and the oil inside of it has solidified when it's that cold. But I'll need to verify that they are hydraulic before I can say for sure.