NSKeyValueObservation.invalidate()は極力避ける

Fatal Exception: NSRangeException
Cannot remove an observer <_NSKeyValueObservation 0x282f97810> for the key path “xxxxx” from <XXXXX 0x28213c9e0> because it is not registered as an observer.
...
0  CoreFoundation                 0x1b0a5927c __exceptionPreprocess
1  libobjc.A.dylib                0x1afc339f8 objc_exception_throw
2  CoreFoundation                 0x1b09634b0 -[NSCache init]
3  Foundation                     0x1b13ff430 -[NSObject(NSKeyValueObserverRegistration) _removeObserver:forProperty:]
4  Foundation                     0x1b13ff1ec -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:]
5  Foundation                     0x1b14bf48c -[NSOperationQueue removeObserver:forKeyPath:]
6  Foundation                     0x1b13fef2c -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:context:]
7  libswiftFoundation.dylib       0x1dee06b04 NSKeyValueObservation.invalidate()
8  *****                          0x1059594e4 (Missing)
9  *****                          0x1059585fc (Missing)
10 *****                          0x105956b90 (Missing)
11 *****                          0x10594a4b4 (Missing)
12 libdispatch.dylib              0x1b0498a38 _dispatch_call_block_and_release
13 libdispatch.dylib              0x1b04997d4 _dispatch_client_callout
14 libdispatch.dylib              0x1b047cafc _dispatch_root_queue_drain
15 libdispatch.dylib              0x1b047d248 _dispatch_worker_thread2
16 libsystem_pthread.dylib        0x1b06791b4 _pthread_wqthread

import Foundation

class MyObjectToObserve: NSObject {
    @objc dynamic var myDate = NSDate(timeIntervalSince1970: 0) // 1970
    func updateDate() {
        myDate = myDate.addingTimeInterval(Double(2 << 30)) // Adds about 68 years.
    }
}

class MyObserver: NSObject {
    @objc var objectToObserve: MyObjectToObserve
    var observation: NSKeyValueObservation?

    init(object: MyObjectToObserve) {
        objectToObserve = object
        super.init()

        observation = observe(
            \.objectToObserve.myDate,
            options: [.old, .new]
        ) { object, change in
            print("myDate changed from: \(change.oldValue!), updated to: \(change.newValue!)")
        }
    }
}

let observed = MyObjectToObserve()
let observer = MyObserver(object: observed)

observed.updateDate()

/* No problem is to call invalidate() repeatedly by the same thread. */
// observer.observation?.invalidate()
// observer.observation?.invalidate()

let group = DispatchGroup()

(0..<10).forEach { _ in
    DispatchQueue.global().async(group: group) {
        /* Leads to a crash by NSRangeException */
        // observer.observation?.invalidate()
        observer.observation = nil
    }
}

group.wait()

observed.updateDate()

observation?.invalidate()
observation = nil