I have a similar issue with the through mount connection on the Mach 2 when I use USB3.  Works fine until we get below a certain temp, then it breaks up.

Some cables work better than others, but I haven't been able to make it completely go away except by changing it to USB 2.  I bought myself a new cold weather USB 3 hub thinking maybe that would help, but it didn't.

What works for me right now is PC->Mach2 mount->Camera->hub->other stuff.  So only the camera is running USB3.  If I rearrange it to PC->Mach2->Hub->Camera then it fails when temp goes below about 5F.