Not every MacBook Pro is capable of driving a 4K display using SST. According to Apple, here are the Macs that can successfully drive a Single-Stream Transport 4K display at 60Hz:
MacBook Pro (Retina, 13-inch, Early 2015) MacBook Pro (Retina, 15-inch, Mid 2014) Mac Pro (Late 2013) iMac (27-inch, Late 2013) and later Mac mini (Late 2014) MacBook Air (Early 2015)