Unable to view labels on a hosted feature service published from ArcMap

Description

When publishing a hosted feature service with labels from ArcMap to ArcGIS Online, the labels do not display in the web map.

Cause

This is expected behavior. When publishing to ArcGIS Online, the labels do not appear in the web map because labels created in ArcMap are displayed differently than in ArcGIS Online. Labels are part of the map document layer properties and do not carry over to ArcGIS Online as displayed by default in the feature service.

Solution or Workaround

The following workarounds are possible solutions for this problem.

Create labels in the ArcGIS Online map viewer

After adding the layer to a web map, create the labels for the features in ArcGIS Online by following the instructions in ArcGIS Online Help: Create labels.

Create feature geometry from the labels using Convert labels to annotation and Feature Outline Masks tool

Note: 
The Feature Outline Masks tool is only available with an ArcGIS Desktop Advanced license. For more information, refer to the licensing information for this tool.

1. Convert labels to a geodatabase annotation feature class. Refer to Converting labels to geodatabase annotation.
2. The Feature Outline Masks tool converts the geometry of the labels stored in the annotation feature class to polygons in a new polygon feature class.
3. Convert the new polygon feature class to a shapefile, and add the shapefile in a ZIP file format to ArcGIS Online. For more detailed steps, refer to ArcGIS Blog: Adding labels to ArcGIS Online web maps: Part 1.

Publish the map as a tile service instead of a hosted feature service to ArcGIS Online

In ArcMap, add the labels to the map and publish the map as a tile service to ArcGIS Online. For more detailed steps, refer to ArcGIS Online Help: Define and publish a map in ArcMap.

By publishing the map as a tile service, the labels added in ArcMap are published and displayed with the data. Once published, however, the labels and data cannot be edited. This is because the tile service consists of tiled images of the map and does not display the label or feature geometry.

Note: 
Publishing a tiled map service consumes credits. For more information, refer to ArcGIS Web Help: Understand credits.