When opening a map in Collector for ArcGIS (Windows), some layers fail to load and the following error message is returned:
This is a known issue. The error occurs if a layer in the map opened in Collector for ArcGIS (Windows) contains a coded value domain with empty values.
Solution or Workaround
Resolve the error by removing the empty domains or adding values to them in ArcGIS Desktop before publishing the layer to ArcGIS Online for use in Collector for ArcGIS (Windows). To modify and delete domains in ArcGIS Desktop, refer to the following document: Modifying and deleting attribute domains.
Domains can also be added and updated in ArcGIS Online through the Data tab in the hosted feature layer's item page. For more details, refer to ArcGIS Online: Define attribute lists and ranges.