When accessing the group configuration for the main category (ID 0) it's not possible to sort the groups registered in this category.

1. From the side menu, click Catalog.
2. Click Categories.
3. Click the category named Categories, that is, the first parent category.
4. Access Actions > Group.
5. On the next page you can view the groups, but the blue bars used to sort the groups are not displayed.

Currently the only solution is to perform the ordering of the fields through a Javascript customization on the front-end.