Hi Pete,
@Rick does have a point.
We have seen some very strange things happen with broken plugins and themes, plenty of times you would never think it can be caused by the theme it it turns out it is. Very easy test is to just switch to the "Boost": theme and clear the cache and check again, this will take you less than 5min. If this does not work, check your plugins, anything that is old, outdated, not supported. If it worked at some stage before, investigate what changed recently on the site.
Let us know if you come right.
@Rick does have a point.
We have seen some very strange things happen with broken plugins and themes, plenty of times you would never think it can be caused by the theme it it turns out it is. Very easy test is to just switch to the "Boost": theme and clear the cache and check again, this will take you less than 5min. If this does not work, check your plugins, anything that is old, outdated, not supported. If it worked at some stage before, investigate what changed recently on the site.
Let us know if you come right.