[abenedik]

I see now that this is a problem in the native assimp exporter - it seems that when exporting to fbx the transformation on the root element is not exported. If you export to some other file format, for example dae or gltf, then the transformation is exported correctly, but this does not work for fbx.

A solution to this problem is to add a parent Model3DGroup or ModelVisual3D, then assign our Model3DGroup to that new parent and export the new parent.