Cancellation email not working for Assign a Task

I am using "Assign a Task" in O365. The Assignee is a SharePoint group.  When one of the Assignees Cancels or Rejects the task, I was expecting the workflow to send out the email under the option "Cancellation email options" within Assign a Task.  However, the email is not being sent.  Everyone in the SharePoint Group does get the task request.  But if one person rejects it, the other people do not get the Cancellation email.  Do you have any idea why?