ArcGIS GeoEvent Extension for Server is unable to return the ObjectID values for queries against hosted feature services published to Portal for ArcGIS secured with Integrated Windows Authentication (IWA) and service content coming from ArcGIS Data Store.
Publish directly to the federated ArcGIS Server site through ArcMap with the option to enable feature access. This item still appears in Portal for ArcGIS similar to hosted feature services, but is able to be successfully queried and updated from the GeoEvent Extension.