When you say, 'The other box and tv does not exhibit this behaviour', do you mean that you have two 360 boxes and the picture is OK on the other TV using the other 360 box?
If so swap the 360 boxes around and see if there is any difference in the picture - if there isn't, but the picture on the other box still displays correctly then it's possible that it's actually your TV settings.
The picture quality may depend upon any TV filters you may be using, local dimming, picture mode, HDMI UHD Color on/off etc
If you state the TV make and model number then other members with the same model may be able to offer more exact advice.
Is the TV doing the upscaling or the 360?
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