I had a similar issue, basically the video was not showing (black screen) but I could see the menus and other elements on screen.
For me, the fix was to disable the 10/12-bit color setting on the TV (In my LG TV it was called "HDMI UHD Deep Color" or something like that). Apparently the chipset on the XG1V4 could not reliably establish the higher bandwith connection on 4K (10/12-bit vs 8-bit colour depth) even with a good quality HDMI cable with ethernet.
I have no issues using the same cable and settings with the PS4. Go figure.
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