is Closures doesn't support custom-observed property in swift ?

[howoften]

i define an observed property, and use observe(_, until: _, changeHandler: _) to get value changed callback,
most of time it works fine, but in iOS 10.3.3, i receive a crash log!
crash description: " *** was deallocated while key value observers were still registered with it";

i declare property like this
class Person {
@objc dynamic var age: Int = 18
}

[howoften]

i notice that you invalidate KeyValueObservation in its changeHandler, is it too late?