I have been told this requires VP9 support which at present is missing from the driver.
This apparently works using the Kaby Lake CPU supports hardware decoding of VP9 (netflix preferred codec) and HEVC along with the hardware DRM Netflix requires
All my equipment is HDCP2.2 and HDMI 2.0
I am in the process of building a new rig and eagerly awaiting the RyZen CPU but if I can't do NETFLIX 4K on a PC I may have to go to a Kaby Lake.
My PC at present
PC running w10, RX480 , Sony STR DN860, LG 4K monitor 27MU67
The same kit runs NETFLIX via a ROKU 4
Roku 4, Sony STR DN860, LG 4K monitor 27MU67