ArcGIS Online Map Viewer is unable to display the point in a hosted feature service that contains only one feature when editing is enabled on the service.
This was addressed in the April 2018 update ArcGIS Online. The fix will only apply to newly published single point feature layers.
For existing feature layers that might be experiencing this problem the spatial index will need to be rebuilt. This functionality was also added in the April 2018 update ArcGIS Online and can be found on the item details page for the feature layer under the settings tab.
対処法
Add a second point prior to publishing the hosted service and delete the unnecessary point after publishing.