As of a January 12th, 2015, we published updates for all of the components that we maintain, as well as updates to many other components maintained by 3rd parties. If you are experiencing issues with a component after migrating your app to iOS Unified API, please first check to see if there is an update available for the component in question. Xamarin Studio and Visual Studio will not automatically download updates, you need to add the new version of the component manually.
If you look at the details page for a component, you can see the date it was published on the left hand side of the page, as well as the iOS-64 tag if it has Unified API Support. If the published date was January 12th or later, and the iOS-64 tag appears, you can safely assume it has Unified API support for Xamarin.iOS 8.6+.
NOTE: There were some components previously published that had Unified API Support for Xamarin.iOS 8.4. There were breaking API changes between Xamarin.iOS 8.4 and 8.6 which meant most components needed to be rebuilt specifically for 8.6.