PO Notification is not on Approver's Queue

Hi,

I have one user, whenever he creates or amends a PO and submits for approval, we can see the Approver in Action History but approver is not getting any notification.

Whenever we reset the PO status and user resubmits it for approval, it goes to same approver and this time notification is appearing on his queue.

I tried to see the WF with View Approval through Workflow, I can see the notification icon there, but when I try to open it, it gives below error:

1. Notification 11959961 does not exist.
2. Notification 11959961 does not exist.

One more thing, we tested this with the user in test instance and issue is not there, notification is appearing for the first time on approver's queue.