I think many broadcasters are now producing programmes in a different format. I’m not sure what the ratio is, but programmes such as Shetland appear as you describe on my Humaxes (2000T, 5000T) and directly on TV. Chances are there is nothing wrong with your settings and not much you can do about it.
It has been filmed in a “semi” wide-screen format to give a more cinematic view.
Nothing to do with a change in broadcast format and nothing needs to be changed in the settings (unless it bothers you that much, in which case you need use the zoom setting on the TV, if it has it, but then you will lose the sides of the image).