As a Pega Mobile Client user, if you upgrade to the iOS 11.3, you will not be able to log in at all with iOS 11.3 and 11.3.1.
Second and consecutive attempts to log in do not work anymore.
This affects all Pega Offline applications and Pega Online applications that use cache manifest.
The bug was not fixed in iOS 11.3.1, as Apple initially indicated. Apple now reports that the fix is planned for delivery in iOS11.4.
If possible, do not upgrade until iOS 11.4 is released.