"{Property} was made unavailable in iOS" in Xamarin.iOS

Several properties, for example in UNMutableNotificationContent, have been flagged with this warning:

[PropertyName] was made unavailable in iOS.

even though these are supported and no such warning is shown on the documentation of the Xamarin.iOS page

I tried to find some information on what this warning means, but without success. Anyone got an explanation what it's about?

This is my code for example:

var content = new UNMutableNotificationContent
{
   Title = "Title",
   Body = "You have 2 tasks for today.",
   Sound = UNNotificationSound.Default
};

Every property is marked with this warning for me. (e.g. '"Sound" was made unavailable in iOS.')