In a recent post from Bokeh.Digitalrev.com, it would seem that Sandisk Cfast 2.0 memory cards would have a compatibility issue with Canon's new flagship camera body, the 1Dx MKII.
Sandisk has openly admitted responsability, and would be actively working with Canon to promptly resolve the problem. It's obviously a blow to both companies, as Canon had selected Sandisk as their supplier for the Free Promotion Bundle of a CFast Card & Reader with every camera purchase.
The complete article... HERE