How do I get fetchAllRecordZonesWithCompletionHandler to work with sharedCloudDatabase? (again)

Question

iOS 10 beta question.

fetchAllRecordZonesWithCompletionHandler fails with sharedCloudDatabase or specifically the zones come up empty. This used to work like last week. I have no idea why it's not working now. I haven't "unshared" anything... I tried sharing a new record again, the share seems to go through but the custom zone (where the record is shared from) that is shared from the private database of user A does not show up in the shared database on user B.

It fails like this on user B:

[database fetchAllRecordZonesWithCompletionHandler:^(NSArray<CKRecordZone *> * _Nullable zones, NSError * _Nullable error) {  
  DLog(@"Got from database %@ record zones: %@, error: %@", database, zones, error);  

  for (CKRecordZone* zone in zones) {  
  DLog(@"A zone with identifier: %@, name: %@", zone.zoneID, zone.zoneID.zoneName);  
  }  
  }  

The output shows that zones is an empty array. No error:

Got from database < CKDatabase: 0x170029680; databaseScope=Shared, container=>> record zones: ( ), error: (null)