Following up on another post regarding grouped layers in Maps Beta. It seems as though when I use the map that was created in Maps Beta (including grouped layers) in Dashboard, only the non-grouped layers appear. I am using ArcGIS Enterprise 10.8.1, is this functionality supported?
The newer version of Dashboards that supports group layer won't be included in ArcGIS Enterprise until version 10.9. Unfortunately the problem you encountered is expected.