Shares of Advanced Micro Devices Inc., which have been on a major tear in the last year, tumbled almost 13% in the last two days as a slew of mixed reviews on the first members of its new Zen chip family spooked investors about the company’s comeback efforts. largest investor even dropped a chunk of shares, as a regulatory filing showed Mubadala Development Company PJSC sold 45 million shares with a market value of $613 million.