Lesson learned ? Do not do this.
Download into an empty model and examine the model for errors before ever inserting into your own models.
Hopefully you can fix this by deleting the instance of the 3DW model (it is inserted as a component.) Then purge all.
If this doesn’t work, turn on all hidden geometry (View > Hidden Geometry), show all layers, and then Edit > Select All, and paste into a new empty model in a separate instance of SketchUp (Windows) or a new document frame (Mac editions.)