FAQ: Why are labels created in an ArcGIS Online feature service not displayed in ArcMap or Flex Viewer?
Why are labels created in an ArcGIS Online feature service not displayed in ArcMap or Flex Viewer?
However, when using the service outside ArcGIS Online as a client application, the label reference information is lost because saving the layer information does not alter the service itself. This is because when layers are saved from the web, references to the layers and the properties that users configured are saved, but not the actual data.
Users may use ArcGIS for Server to create permanent labels in a service.