Seems to happen randomly and has been happening for years with no solution. Exporting from Archicad and importing to twinmotion randomly does not bring the entire model in. Every single project has something missing, a piece of handrail here a roof there, it's really annoying.
Hello ,
Thank you for posting in the community and reporting this issue. In order to fully investigate the problem would you be able to submit a bug by following this link: https://twinmotionhelp.epicgames.com/s/case-community-page
Kind regards,
Vincent B.