The reverse geocoding operation executes on the World Geocoding Service instead of the custom locator in the Crowdsource Reporter web app when selecting a location in the web map.
Reverse geocoding in the Crowdsource Reporter app is designed to use the World Geocoding Service by default (if no service is configured in the organization). If any geocoder is configured in the organization, the first geocoder from the organization's geocoder list will be used. So if users want to use any custom geocoder for reverse geocoding, the locator should be configured as the first geocoder in the organization (organization settings) geocoder list.