Able to say what spec the wall or test cable is? High Speed min req for 4k. Just to be sure.
I get a spluttering signal on Standard HDMI. My 4k are either high speed or Premium High Speed (cheap ones). But are short.
@KennyA1 If it works on your main TV with the less from your other TV, then it's older spec HDMI leads
Solution after discussion with Samsung - needed to use a max length 2m hdmi cable so need to reposition box and possibly tv - but temporarily fixed so all good. Just need to plan redecoration now - thanks all