Projectors don't have accurate 3D models, they are pretty much just a cuboid. If you turn it on in a live view you can see the orientation.
Unless you mean you get the selection box but no model? If you've removed your current layer from the filter applied to a view then it when you drag anything in from the library you will get the selection box it will look like the fixture doesn't physically exist, but if you look in the fixtures tab it will be listed there.
Remove the filters from your views, or re-add the current layer to your active filters.