It doesn't surprise me... Sottozero and Pilot Alpin tires are not good in really bad winter conditions. They are "ok" in mild winter or on fluffy, powdery snow. On slush, ice and wet snow they are pretty useless IMO... similar to an all season tire. The are just too dry road performance oriented... you have to compromise in one area of the other.
2016 M2 | Long Beach Blue | 6MT - current
2015 M4 | Austin Yellow | DCT
2014 Corvette Stingray | Z51 | Torch Red | 7MT
2012 MB C63 Coupe | Performance package | Obsidian Black
2011 E92 M3 | Jerez Black | Fox Red | DCT | Competition Package