Hello ,
Thank you for posting your question in the community and this behavior does seem strange. If you are using a keep hierarchy collapse method you will get more meshes and geometry. We would need to investigate this and was wondering if you were using the Datasmith Exporter plugin to bring in your scene into Twinmotion?
Here is the link to report a bug:
https://twinmotionhelp.epicgames.com/s/case-community-page
Kind regards,
Vincent B.