urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) does not trigger

I have an app that used to work fine until WatchOS 4. When upgrading to WatchOS 5 (now beta 3) it stopped receiving urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession).

This is how I used to schedule the URLSession

func scheduleURLSession() {
      let backgroundConfigObject = URLSessionConfiguration.background(withIdentifier: NSUUID().uuidString)
      backgroundConfigObject.sessionSendsLaunchEvents = true
      let backgroundSession = URLSession(configuration: backgroundConfigObject, delegate: self, delegateQueue: nil)
      print("scheduled background session: ", backgroundSession)
      let downloadTask = backgroundSession.downloadTask(with: sampleDownloadURL!)
      downloadTask.resume()
   }

func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL)

Never happens as well.

Any help would be great.