NSMetadataQueryDidUpdateNotification not automatic

NSMetadataQueryDidUpdateNotification is not triggered automatically. On my iPhone 4s with iOS 9.3.5 it triggers automatically, in none of the simulators (some running iOS 9) nor on my other iPhones nor tablets does it trigger automatically. It will not trigger unless on each individual device I push a .sync file to iCloud.

Any ideas why?

if (self.metadataquery == nil) {
     self.metadataquery = [[NSMetadataQuery alloc] init];
     self.metadataquery.searchScopes = @[NSMetadataQueryUbiquitousDocumentsScope];
     self.metadataquery.predicate = [NSPredicate predicateWithFormat:@"%K.pathExtension = 'sync'", NSMetadataItemFSNameKey];
}
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(iCloudSyncChange:) name:NSMetadataQueryDidUpdateNotification object:self.metadataquery];
[self.metadataquery startQuery];

- (void)iCloudSyncChange:(NSNotification *)notification {
     NSLog(@"iCloudSyncChange: %@", notification);
}