I've had the greatest minds in the country working at this sidebar text. I tried everything that made sense and clearly the answer lies in the realm of nonsense. Another 2-3 hours spent this morning dithering over what to do. Then I fidgeted, went into 'fonts and colours' under 'Layout', clicked on 'revert to template default', then 'save changes' and lo and behold the text is back. I wanted to change the colour of the text but I'm not touching anything. I still don't know if this is permanent or just a temporary solution. But I am briefly satisfied.