persistentIdentifier not saved for Siri Shortcuts using NSUserActivity

I'm adding Siri Shortcuts to my app using INUIAddVoiceShortcutViewController and things are working fine, except when I try to delete a shortcut using NSUserActivity.deleteSavedUserActivities(withPersistentIdentifiers:)

I verified the persistentIdentifier is not being saved for the NSUserActivity. Below is the code that I used to create the NSUserActivity:

    func createUserActivityForShortcut(workoutName: String, timerID: String) -> NSUserActivity? {
        
        let userActivity = NSUserActivity(activityType: "com.fourthframe.intervals.start-timer")
        userActivity.isEligibleForSearch = true
        
        userActivity.isEligibleForPrediction = true
        userActivity.suggestedInvocationPhrase = "Start \(workoutName)"
        
        userActivity.title = "Start \(workoutName)"
        userActivity.userInfo = ["timerID": timerID]
        userActivity.persistentIdentifier = timerID
        userActivity.needsSave = true
        userActivity.requiredUserInfoKeys = ["timerID"]
        userActivity.becomeCurrent()
        
        return userActivity

    }

Is this a known issue or did I do something wrong?

Thanks,

Jeff