I solved this issue with link in your answer, but after that I had one more issue and it was about a signature widget. I could not create a signature. I just removed the plugin cordova-plugin-wkwebview-engine-nextgen from config.xml and now everything works fine. I can run the application on iOS 11 and all widgets work properly.
As Danny mentions here, you need to bump up the version (spec) of the wkwebview-engine plugin to v1.1.0. In your phonegap config.xml file:
<plugin name="cordova-plugin-wkwebview-engine-nextgen" source="npm" spec="^1.1.0" />