I have published a hosted feature service from a file geodatabase twice using ArcMap 10.5. The first feature service would not download to Collector (version 18.0.1, build 1031) with the error "Unable to construct a WebMapLayer". I checked the geometry of the desktop geodatabase, separated one point with sub-domains into two separate points (in case the sub-domain was causing a problem), and published again as a new feature service. I still cannot download this feature service, but now get the download error ""Unable to create replica. Please check your parameters., Create replica internal error.". The service is visible and editable online.