This has been reported by Pega to Apple as Bug: 38505756, and thanks to Pega, Apple fixed this bug in iOS, but the fix will be available in iOS 11.4
Pega Mobile Online applications are affected only if using cache manifest.
Pega Mobile Offline applications are affected, and will not work offline at all.
When login in, even though Pega application properly authenticates the user, WKWebView does not send cookies along with cache manifest request and all the requests for resources listed in it. Because of that, application cannot be properly cached and installed. This is a regression comparing to all previous versions of iOS.