In POA provider's panel Top > System Director > Notification Manager > Notifications log (since POA 5.5 Operations > Tasks > Events) is empty for some staff members.
Notifications have not been configured for the staff member. It is only possible to configure notification settings per staff member in current versions of POA.
In order to get the notification for a staff member you need to configure the notification subscription for this staff member. Please refer to the POA Provider's Guide.
There is a feature request to allow configuration of global notifications subscriptions in POA, internal ID is POA-79027.