I am using ArcGIS Pro 2.1.0 with utility network data model. I have added couple of subtypes for assembly FC. If I try to delete one Subtype using 'remove subtype' tool, OR with 'create/manage' pane of subtype and save it, it fails with below error.
ERROR 002140: The subtype is required by utility network. Failed to execute (RemoveSubtype).
There are no custom domains assigned to it. Am I missing something to remove/change before removing subtype?