Asked to report this as a bug:
When importing via an assetContainer, instances appear as soon as the import is finished, without waiting for assetContainer.addAllToScene(). This may be a broader issue with createInstance() not being aware of multiple scenes/scene-like-objects.
Edit: Here’s the Blender (bForArtists) file to illustrate the scene’s construction and hierarchy: Dropbox - TriColumn.blend - Simplify your life
The root mesh in my model is a null/empty/transformNode–a model with no geometry. I tested whether this might be causing issues, but parenting everything to an ordinary mesh doesn’t change anything.