WBW products not defaulting to best selling when put on top

Hello,

We we are currently investigating an issue where the sort filter does not default to sorting the products by “best seller” when put at the top of the filter bar it defaults to an A-Z sorting. But we want the products to sort by “best seller” as soon as u enter the “shop” page. However, the filter works correctly when placed under A-Z. For example

Sort by “A-Z”

and when changing this to sort by “best seller” it sorts the products correctly. its just when moving the “best seller” filter category to the top and wanting it to default to that type of sorting that the problem occurs.

Thanks in advance!