SFRA navigation menu - category sorting

Hi all,

I am using the SFRA storefront and am having an issue with the sorting of the categories in the main navigation (menu.isml).

I can rearrange the categories directly in BM and the ordering reflects as expected in the navigation menu. However, during the next product import cycle (2 times per day, from an external data source) my manual reordering is reverted to alphabetical.

I suppose I need some kind of sorting rules for categories (NOT the products they contain) but I can't seem to find that.

How is the navigation menu sorting of categories usually handled?

Thank you.