Problem: Unable to view labels enabled for hosted feature services in the Collector for ArcGIS application for Android and iOS
Labels enabled for a hosted feature service using the Create Labels option in ArcGIS Online do not display when the same hosted feature service is accessed in the Collector for ArcGIS application for Android and iOS.
This is a known limit.
Solution or Workaround
To view labels in the Collector for ArcGIS application, label the map in ArcMap instead of ArcGIS Online.