The cache is not at the published coordinates.
The Hidden History of St Ives Bonus Cache is hidden following the theme of the Adventure Lab Cache which you will need to have completed to obtain the coordinates. It was originally hidden on a nearby structure which fitted the theme of the lab cache but had unfortunately been muggled twice within a short space of time.
Final Coordinates are: N52 19. ABC W000 03 CDE
Coordinates should add up to 52