When running a report the feature map does not display: it just shows the feature and an empty map.

The feature map is one that I've created in Portal for ArcGIS. The web map itself and all of its layers are shared with everyone. All the layers are in the same spatial reference but it is not Web Mercator. Does this need to be?

If I change the feature map to be the Topographic one from ArcGIS Online then that does display OK, but I would like to use my own web map from Portal.