FYI - Had this problem fixed by helpful service manager on the phone. Ref pages 123 and 92 of owners manual. The whole system can be switched off by setting on the headup display under settings (Tailgate on/off). Head up is the box screen in front of the driver NOT the large screen. Using right side of steering wheel buttons, go right - right - right until Settings then up/down until "Tailgate ON' then the middle dot to select. I don't know how it got OFF but tried lots of useless things on the web before discovering RTFM.
