The reason the users are getting these is because a configuration on the Workflow Mailer called "Send e-mails for canceled notifications" is enabled. The way that feature works is if a Notification is sent to a user at 11:00 AM today for example to approve a Purchase Order, but that notification is closed or cancelled (maybe they responded via their worklist for example or
someone else processed it via Forward Documents form, etc.) then this notification that is confusing them is sent, that the previous email can be ignored.
To disable this feature please do the following :
1) Login to Oracle Application Manager (OAM) via System Administrator > Oracle Application Manager > Workflow
2) Edit the Workflow Notification Mailer service by clicking on the Edit button.
3) Navigate to the Message Generation stage and will see this parameter called : "Send e-mails for canceled notifications"
4) Uncheck the "Send e-mails for canceled notifications" check box and click on Finish button complete the changes.
This feature used to exist in earlier application Releases before OAM with profile option: WF: Mailer Cancellation Email
Reference Note 280023.1 "How Do We Stop The Email Notification Cancellation Email Messages? "