Having some odd problems since buying an Xbox One X with the ue49ks8000t television..
I have upgraded to the latest firmware as of December 2017 (I had to do this by usb as the TV wouldn't find the new version). Version 1208
I have turned on HDMI 2 to UHD and have 4k and uhd both working and recognised by the Xbox and the TV.
But the picture is dull and muted at times. The TV keeps dimming the picture. If you go in settings and reset the Backlight the picture brightens again but this lasts about 1 Min before it mutes/dims again.. Even though it still says Brightness 20.
The other thing is if you play a game like Star Wars Battlefield 2 the bright lights tend to glare and bleed on to other images on screen
The whole thing just doesn't look good.