Grouped Products not added to Woocommerce Cart

Hi, I have lots of grouped products and when I add the individual products from the grouped products page they don’t always add to the Cart. Normal products are fine and sometimes adding from the grouped products page does work. The problem seems to occur when there is already something in the Cart and as I say it doesn’t happen every time. When the problem happens the cart total at the top appears to go up (with the new products added in) but when you go to the Cart the total is back where it was and the new products are not there. I have excludedeBasket and Checkout pages from cache.
I’m using Flatsome Theme. Any ideas? It is working really well otherwise.

Regards
Janak