Hi terrco ,
Sorry for the late response.
We haven't been able to test your issue in a multisite installation until now.
We've just followed the steps described in the knowledge base article you liked in your last post. It worked for us. After assigning all the atum permissions to two users (one with the site administrator and the other with the shop manager roles), both could see ATUM in the menu and access all its pages. In case it had anything to do with where we assigned permissions, It was done from the single site's dashboard.
Would you be so kind as to recheck the permissions?