Stock quantity update on product page with variant change - Studio 2.0 theme

Example product: https://snpos.learay.co.uk/products/bear-island-tee-orange

If you change the size you will see the SKU changes at the bottom of the page, but the In Stock figure doesnt. I have managed to figure that out following another post, however I cannot figure out how to do the same thing with the In Stock figure?