title: Sometimes VNDetectFaceLandmarksRequest fails with unspecified error
body: <p>In my iOS application I use VNImageRequestHandler and VNDetectFaceLandmarksRequest to identify face bounding box and pupils. In my log server I see an error:</p>
  <p>Error Domain=com.apple.vis Code=9 encountered an unexpected condition: Unspecified error .</p>
  <p>It looks like this error only occurs to <strong>some users</strong>, but for these users it happens multiple times. I couldn't find in the Apple's documentation any way to obtain more data about this error.</p>
  <pre><code>let imageRequestHandler = VNImageRequestHandler(cvPixelBuffer: pixelBuffer, orientation: .leftMirrored ,options: requestOptions)
  do {
      try imageRequestHandler.perform([faceDetectionRequest])
  } catch {
      LOG(error) // send log to server
  }
  </code></pre>