FYI - I just successfully completed a whole series of flats, bias and dark sequences using the ASI 1600MM-C and USB3, without a single hang up. The problems that I had last night with USB3 must have been either:
1. A result of using the SGP Frame and Focus tool or
2. A result of simultaneously using other programs, namely PHDs and CDC. But the camera was the only USB3 device that I had, so I don't understand why there would be a conflict.