@pekka.varis -
Could you share Create logs from when you try to assign material and it failed?
Also, can you do one test for me? close Create, Reopen Create, then open the base USD file with the converted FBX interior. With doing minimal actions, select the chair and try and assign material. Try not to do anything else, move, scale, add, etc…
Also, did you try what @mirice mentioned above? We are trying to figure out at what your process was so that we can get the error to reproduce on our end.