workflow approval mail issue

Hi experts,

We found an issue about workflow mailer.
The approvers received the approval emails from ebs(12.1.3). They aprroved or rejected through emails.

But the approval notifications still exist in their user's woklist.

Approved the notification through Email. But the workflow did not update the workflow notification's approval status.

I also helped them to check the workflow, and the workflow has no approval activities.

The applicants also did not receive the approval email from ebs and the expenses are still waiting approval status.
It seems that workflow can not received our approval result's email.

*It depends on which approver's user.(specific user)   Some users don't have this issue.