Swift fileCoordinator hangs application

Question

I have the following function which deletes a file (happens to be iCloud). Sometimes it works, other times it hangs at the filecoordinate.coordinate line:

func deleteDocumentAtURL(url: NSURL) {

    print("IN DELETE: existing url: \(url)")
    print("IN DELETE: openable: \(itemIsOpenable(url as URL))")

    let fileCoordinator = NSFileCoordinator(filePresenter: nil)
    print("IN DELETE: attempting file coordinator, might get STUCK here")
    print("IN DELETE: file coordinator = \(fileCoordinator)")

    var fileError: NSError?        

    fileCoordinator.coordinate(writingItemAt: url as URL, options: .forDeleting, error: &fileError, byAccessor: { (urlForModifying) -> Void in

        print("IN DELETE: modifying URL: \(urlForModifying)")

        do {
            print("IN DELETE deleteDocumentBlock")
            try FileManager.default.removeItem(at: urlForModifying)

            print("IN DELETE: deletion OK")

        } catch let error as NSError {
            let alert = UIAlertController(title: "Error deleting", message: error.localizedDescription, preferredStyle: UIAlertControllerStyle.alert)

            alert.addAction(UIAlertAction(title: "Done", style: .default, handler: nil))

            self.present(alert, animated: true, completion: nil)
        }
    })
    print("Error code = \(fileError)")
    print("IN DELETE: at the end")
}

the itemIsOpenable function checks the iCloud download status as follows:

func itemIsOpenable(_ url:URL?) -> Bool {

    // Return false if item is nil
    guard let itemURL = url else {
        return false
    }

    // Return true if we don't have access to iCloud (which means
    // that it's not possible for it to be in conflict - we'll always have
    // the latest copy)
    if DocumentListViewController.iCloudAvailable == false {
        return true
    }

    // Ask the system for the download status
    var downloadStatus : AnyObject?
    do {
        try (itemURL as NSURL).getResourceValue(&downloadStatus,
                                                forKey: URLResourceKey.ubiquitousItemDownloadingStatusKey)
    } catch let error as NSError {
        NSLog("Failed to get downloading status for \(itemURL): \(error)")
        // If we can't get that, we can't open it
        return false
    }

    print("item is openable download status = \(downloadStatus)")

    // Return true if this file is the most current version

    if downloadStatus as? String == URLUbiquitousItemDownloadingStatus.current.rawValue {
        print("download status = \(downloadStatus)")

        return true
    } else {
        let currentStatus = downloadStatus as? String
        print("current status = \(currentStatus)")
        print("Ubiq status = \(URLUbiquitousItemDownloadingStatus.current.rawValue)")
        return false
    }
}

The print output when the app hangs is as follows (it goes no further):

IN DELETE: existing url: file:///private/var/mobile/Library/Mobile%20Documents/iCloud~net~thesavorys~Notes/Documents/Document%201997293854.note

item is openable download status = Optional(NSURLUbiquitousItemDownloadingStatusCurrent) download status = Optional(NSURLUbiquitousItemDownloadingStatusCurrent) IN DELETE: openable: true IN DELETE: attempting file coordinator, might get STUCK here IN DELETE: file coordinator = NSFileCoordinator: 0x17046de40

Any thoughts of what is happening here much appreciated...

Thanks Tim