Hello,
Some people are unable to approve due to the email and notification disappearing. We just ran another test trial, and the user got a notification on her Jira app to approve a work item but then disappeared immediately after. The same goes for the email notification on outlook. Out of the two people unable view the approval message, one is a Jira/JSM admin and agent, and the other is a Jira Service Management customer on our service desk.
I already looked at the customer notification settings and they look fine. Any help is appreciated!