Using UIWebView on an iPad Pro (iOS 9.1) gives you a wrong userAgent, because it says its an iPhone.
You can reproduce this behavior with the iPad Pro device and with the iPad Pro simulator. In both cases the userAgent is:
This seems to be a known bug with iOS 9.1 on the iPad Pro because it is fixed with iOS 9.2 beta 4 and you are getting the right userAgent.
If you clean install your app, everything works fine on iOS 9.2 beta 4. But if you update your previously installed app, you are still getting the wrong userAgent because the CDVUserAgentUtil uses the cached userAgent.
For users it is not possible to clean install the app, because in that case the whole configuration would get lost. To get the right userAgent every time, developers must have the option to disable the caching of the userAgent in their apps.