Hi April.
This is a known issue visible here: Unreal Engine Issues and Bug Tracker (UE-66985) and that should be fixed in one of our recent Datasmith hotfixes.
Please make sure to update to the latest Datasmith version for the UE 4.21 release. This includes updating both the Datasmith importer plugin in UE4 (via the Epic Games launcher), and the Datasmith exporter plugin in Revit (available here: Datasmith - Unreal Engine)
I hope this helps.
For all future Unreal Studio/Datasmith issues or questions, please be sure to log your issue to our dedicated Unreal Studio support site - https://unrealstudiohelp.epicgames.com/s/case-community-page
Thank you.