NSUserActivity persistentIdentifier not persisted

Setting persistentIdentifier on an instance of NSUserActivity is not persisted. The activity shows up in spotlight as expected but has a persistentIdentifier of nil (confirmed in onContinueUserActivity).

Moreover, the NSUserActivity.deleteSavedUserActivities(withPersistentIdentifiers:) has no effect (the activity still shows up in spotlight search), which I guess is caused by the persistent identifiers not being persisted in the first place.

Any ideas? Thanks.
NSUserActivity persistentIdentifier not persisted
 
 
Q