Very Nice Dave!
Do you have 2019 loaded? If so I think there is an issue with Revit 2019 and IFC's. After the IFC is bound, I haven't found away to Ungroup it, as I can't even select objects from the IFC (Flex+Grilles).
There may be a way I'm just not fluent enough in Revit yet.
Let me know if you can. By the way Revit 2018.3 worked as you describe.