I read mostly good thing about Spyderco. Perhaps it's a bad heat treat? Lot's of their other S30V are reported doing very well ... If you don't mind, send to them for inspection.
The K631 is so nice in the hand, although the weight of the handle is too much to the rear. Pinching the blade by the choil & thumb ramp you'd feel the weight 'pulling' it backward. The praise should still go to Spyderco as original designer. One day ... I might just get one. Endura 4 ZDP189 here is sold at 300$ (US$!).