If an instructor enters grades for an assignment or quiz with an automatic grade-posting policy, students with notification preferences set for email and push notifications will receive both an email and push notification. 

But if the assignment has a manual grade-posting policy, students will receive only an email and not the push notification when grades are posted. 

In case #07526980, Instructure support explained that while entering grades will trigger a push notification, posting grades will not (see the Notifications guide).

At The Wharton School, all courses have a manual grade-posting policy by default, a feature our faculty have wanted for years. The limitation of push notifications for posted grades makes the mobile app much less useful for students who want to check their grades on the go. Please consider supporting push notifications for posted grades.