From: http://www.gamesas.com/topic/1344939-things-disappearing-in-the-world/page__st__60
I've done some additional tests and here's what I know that might help, this appears to be a memory/loader issue; it's definitely a bug. The solution for the CK tap 1 a few times to cycle the object visibility that will bring it back. OR tap F5 to refresh the render window that will also bring it back into view. Anytime you use the door marker to go in and out, your house will disappear again, just tap F5 again to reload it.
In game, walk or ride to your location. Fast travel can result in the same memory loader error and the structures will be invisible. Entering an interior and returning may force reload the game version
Hopefully we'll see a fix for this in the next update, I'm certain devs are aware of it's existence.
-and-
Someone found out that the meshes disappear after fast travel only if their "size" value is greater than 1024:
Thought I'd mention it, as we now have a concrete target.