Workspace : notification mail are not send if changeable preselection is disable
Test in typo3 8.7.6
Case : you use workspace notification and Default notification mail recipients
If you disable "changeable preselection" no mail are send to all selected "Default notification mail recipienrs", but mail are send to other users who are manualy selected by the user when stage change.
But if you enable ""changeable preselection" mail are send correctly to all users