Using Group By and Sort on a list view - not working if sort and group fields different

I have a modern site with a list containing the fields Business Function, Category and Order ID. 

I wish to view the items in groups by Business Function and Category but I do not want the sort order alphabetically for Business Function, so I have introduced and Order ID for the sort. But it appears that this will not work, does anyone know if this is a bug, limitation or have a work around other than adding the order id to the Business Function. 

Here is my list data and the list view details :