Hello ,
Thank you for posting in the community regarding your import issue. We would need to look at your Rhino file to better understand if the the problem is with the OBJ format or something else. You can report a bug by following this link: https://twinmotionhelp.epicgames.com/s/case-community-page
As a workaround try to bring in the content from Rhino using the Datasmith Exporter plugin, with Direct-Link or udatasmith format as that might have better results.
Datasmith overview article and video:
https://twinmotionhelp.epicgames.com/s/article/Getting-Started-using-Datasmith-Workflows-with-Twinmotion
https://youtu.be/mHzZml2yxn4
Hope this helps and please contact us so we can best look into this problem.
Kind regards,
Vincent B.