A:Answer As an X85J owner I can confirm that when using HDMI 2.1 port for input, on 120Hz 4K vertical resolution is cut in half and upscaled.
If you are running internal content (youtube, netflix,etc) this is not the issue.
Problem is not in cable, it is in SoC used for input signal processing.
This issue is also confirmed on multiple testing sites and forums (rtings.com and official bravia forum).