Help! When using iCloud Numbers, all text has disappeared from the formula bar itself?

When typing a formula as normal in numbers, the text is not showing... the curser shows text is being typed, but no text is displayed in the formula bar... its as if I have somehow changed the font to white colour!!!!

Also, when I select a cell with a pre-exisiting formula, again the text is not displayed within the Cell 'Bubbles' in the formula bar...

Everythign was fine up until a few weeks agi, and the issue has only recently occurred when logging into iCloud using a Windows PC... everything is fine on my iPhone and iPad...