Pre-Approval FYI & Post Approval FYI Not work as expected

Summary

Pre-Approval FYI & Post Approval FYI Not work as expected

Content

we used three stages

1. Preapproval FYI : we use it to send FYI notification to employees in approval group members when PO submitted from buyer and it worked fine but when users in approval group take any action , the other users not receive FYI notification that document approved , rejected or returned,why? i expect it to work like when PO submitted so what is the difference?
2. Terms Approval Serial : we use this stage for serial approval and it worked fine
3. Postapproval FYI : we use this stage in order to send FYI notification to users in approval group when the document implemented , rejected , returned,etc.. but it not work , the notification that the PO implemented or rejected sent only to the buyer and we need it to be sent to all users in approval group??