When you configure the pop up in the web map it shows the clustered point details, and then the individual point details when you zoom in. This functionality is extended to the (newly added) popup within the map element of the dashboard, however this functionality is not extended to the details element of the dashboard which is based on a layer's popup information (as stated here: Details—Operations Dashboard for ArcGIS | ArcGIS). Please extended the clustered point popup details to the Details element of the dashboard.
