As explained by Taiwanese sources, the development of chipsets for processors Zen was entrusted to ASMedia company, and that there were problems with the implementation of support for the USB 3.1 interface. A certain defect leads to the transfer of the integrated controller forces the information rate fall, so to solve the problem have to use a "bypass" scheme with additional discrete components or rely on "external" USB 3.1 controller. Naturally, the cost of the motherboard it affects not the best way.
If we believe the rumors, AMD is ready to buy all the necessary components to work on the bugs at his own expense, and to make them available to manufacturers of motherboards, along with a set of system logic for Zen processor performance Socket AM4. As is known, chipsets family Promontory offer support not only USB 3.1, but SATAe, and NVMe. Bulk supply of appropriate chipsets will begin in the fourth quarter.
Add that ASMedia representatives denied the existence of any problems in his articles for Zen processors. Promontory chipsets have passed all the necessary tests and received certificates. AMD also refused to comment on the situation.