Symptoms or Error
Secure Mail makes use of a notification called a silent notification which is delivered to the application to indicate that new data is available on the server.
On iOS 11, these notifications are not delivered to the app. As a result, Secure Mail is not able to sync new data from the server in order to show notifications on the lock screen.
Solution
There is an Apple bug (33278611) currently tracking this issue. This article will be updated as more information becomes available.
Problem Cause
The root cause of the issue is a regression in iOS11.
Notifications that are designed to indicate to the app that there is new content to sync from the server are not being delivered to the app.