(Vivaldi browser but also tried on Chrome, same results) In a category with a lot of articles, it will not allow me to reorganize them. If I change the setting (A-Z etc) or arrange them manually it will attempt to change it and almost immediately revert it and the "save" icon in the corner will be a red triangle with a !
Move several articles into a new category via the drag and drop feature (a couple dozen at least) and open the category, go to article management, and attempt to change the default organization or rearrange them manually