I recently picked this tv up & so far has been working ok until over the weekend i was playing Halo on xbox one x and i got a Black screen while in game for about 3 secs or so and it returned. Also i have a amazon 4k fire stick which got a black screen today while watching FUBO tv. Is this a HDCP issue ? I have had Handshake issues with a old samsung and PS 4 Pro with the same kind of issue with 4k content.
You could try reconnecting the devices and also check to see if another (known working)cable does the same thing(produces a black screen). Does the TV have any firmware updates pending? You might need to adjust the region in case you're not located in UK.