Hello ,
Thank you for posting in the community about this issue. I am not sure what could exactly be happening without further testing some of the files causing theses problems and recommend you report a bug so we can properly investigate. https://twinmotionhelp.epicgames.com/s/case-community-page
Here is what you should be seeing when opening older files:
It is important to remember that when working with any newer version and it is not possible to again open it in any previous version since it says None and will try to convert but nothing will happen. Thus it is important to save a copy when working with different Twinmotion versions.
If you are working with multiple versions it is best to use shortcuts or the epic games launcher to open the right Twinmotion version, then opening the Twinmotion scene from the File > Open menu.
Hope this helps.
Kind regards,
Vincent B.