I've got a similar problem.
I created, just to get into the CK, a little extension to Vindrel Hall, the house in Markarth.
In the CK it looks like this: http://i.imgur.com/jOWta.jpg

And ingame: http://i.imgur.com/qFJMY.jpg
http://i.imgur.com/kCt8p.jpg

Anyone knows how to fix that?

So it's not just with exterior cells? [censored] hell.
djjojo, does it show up again (in the CK) if you press F5?

Did you add reset [sorry i didn't mean to suggest there is a reset button to use but rather, you have to add a roundbound and set the portal to an existing roombound or extend a roombound to encompass the new addition] the roombound? Doesn't look like it. This is different than what others are dealing with.

This is pretty much exactly what I was dealing with. Try deleting and re-entering the cell right after the door. I had a section with a short hall, a stair, a turn and another stair. When I replaced the cell right at the beginning of the hall the rest of the staircase system magically reappeared in game.

Thanks! I got it.
Maybe I should read Bethesda's tutorials and not do "try and error"

Can you guys test this and see if you see it?
http://steamcommunity.com/sharedfiles/filedetails/?id=8494

I don't see it by fast travel to it (to it as in to Clearspring Tarn), maybe someone else has some more luck

Unfortunately I'm at work, but if it isn't tested by the time I get home I'll give it a go.

Nothing wrong with trial and error.

The roombounds/portals are an optimization feature and not necessarily a requirement unless you're working on something big and complex or editing an existing interior. If you're doing something big and complex then it helps keep the frame-rate up and if you're editing existing interiors the chances are high that they have roombounds and portals setup so you'll have to tie into those existing ones.

Just loaded that save where my house wouldn't appear... and it did.
I can't isolate this issue.

Anyone got any ideas on this?

Someone mentioned in another threat about moving the Mytic Dawn museum in Dawnstar back a bit, along with everything attached to it. When running the game the banners did not move. One answer was something to do with Havok not updating the cells for a long time. Perhaps something to do with that? I'm not too familiar with Havok.

This issue of stuff disappearing in-game even though it's perfectly visible in the CK was reported during the beta but no real solution was found.

I'm currently experiencing this with the alt-start mod I'm building. My shipwreck site loads everything EXCEPT the ship itself and the iceberg I put under it, which makes for a less than stellar experience. The farmhouse I placed in a totally different area sometimes appears, sometimes not. None of these refs have scripts attached to make them vanish. They were placed by dragging them out of the items menu.

I've even tried deleting the offending objects, saving, closing the CK, then reloading and placing all new copies at the same coordinates. Only to have THOSE produce exactly the same behavior. Also moving them slightly doesn't help either.

Re: The Dawnstar issue in that other thread, that's not the same thing as this.

Did Bethesda not think that maybe the random disappearance of every large mesh might be a problem for nearly all worldbuilding mods?

Well it's partly because the whole thing is intermitent at best. Sometimes stuff goes missing, sometimes not. It just so happens that I have 3 objects that ALWAYS go missing, and one that decides that on its own terms.

That is, until the "Is Full LOD" checkbox was suggested to fix it, which may or may not give Bethesda somewhere to go with this.

I don't know if there is a link but only big objects with door / cave link to an interior cell disappeared in an intermitent manner for me. All other objects worked perfectly.

It seems only to affect objects that are very large.

Would one define a farmhouse as "very large"? I could see calling a shipwreck and two iceberg pieces that, but not a farmhouse.

It would be relative. When designing a model there are details to consider. Even a very small object mass wise can be a very large object data wise depending on how detailed it is. I would guess that there are more textures, maps and shapes in a farmhouse than some of the shipwrecks I've seen in game. So, are they (Beth) considering very large in a mass definition or a data definition.

I ask because I haven't looked deep enough yet to know the answer myself. This will be my first modding experience, well on the creators side of it anyway.

Seems to affect anything bigger than a small farmhouse.

Yeah, mine's a farmhouse with a blacksmith.

Gee, I've got no probs with CK so far. Only if I could say the samething about HRT pack. And CK is suppose to be Beta.

This appears to be true for the most part. I've had some dwarven platforms disappear once too.

Yes, I was about to say, it seems partly based on the physical size of the objects. The objects that dissapear on mine are the L-shaped farmhouse, the inn farm building and the blacksmith farm building.

Add me to the list of house mesh not showing up in game.

I've got an another worldspace mod and I'm starting to see some wacky behaviour such as this. One, I've placed a dock and ship in Skyrim. When you enter the ship and leave, it will disappear, yet the doors to the interior remain.

Edit: It's before my coffee so I'll clarify. The ship is the large variety and works normally at first. Entering will cause it to disappear (no scripts attached)