Clicking a Filter Gives Me Spinning Grey Ball

Please help, clicking any of the filters on this website results in a spinning grey ball, with also no products being shown.

So, for example I go to https://www.frenchfurniturefittings.co.uk/product-category/handles/

and all of the products are shown

If I click one of the filters on the left hand side, we get a grey spinning ball and no products shown.

The page I need help with: [log in to see the link]