Invalid expiration email trigerred for approved Resignation transaction

Summary

Expiration email notification is sent to worker even though Resignation was already approved

Content

We were notified of a few cases when an invalid expiration email was sent to employees.  These employees submitted their resignation via ESS, the manager approved within a couple of days, way before the deadline.  We have  the approval flow set up so an FYI notification is sent to the HRIS mailbox once the manager approves a resignation.  The expiration email notification was sent to the employee 7 business day after the transaction was approved. 

Is this a system glitch or do I need to change something?