Hi Ian,
i thinks what Ying meant to say is that the Cart is NOT from GP 🙂
Just a note, Cart icons and menu carts generally get their data from fragments cached in the Woocommerce Transients.
In Woocommerce > Status > tools, there is an option to clear the transients, otherwise they automatically clear after a certain amount of time.
You may also need to force the browser to get the latest data, apart from clearing its caches, adding and removing items from the cart is generally enough to make it request new data.