Both the Site Collection features group and the Site features group have a button that activates the Group Approval. How are the two buttons different?
To ensure that Group Approval works properly, you must activate Group Approval feature on the Site Collection features page first and then on the Site features page. If the solution is activated on the Site features page first, Group Approval will not work properly. To deactivate Group Approval, follow the sequence in reverse. Note Group Approval can be activated only in the top level site of a site collection.