Model vanishing in game

I have a feeling that this question has been asked before, but I
couldn't find any solution after searching through the forum and
tutorials.

I have several models placed in my map, and most of them look just fine
in game. However, there are a few of them that disappear after I
load up the map. To be specific, there are a few stair railings
that are causing problem.

When I walked around in the map, I can feel their presence (because
they clip my movement) but they are otherwise invisible. I tried
moving the model up and down slightly to see whether that solves the
problem, but it persisted. And these invisible models look
perfectly okay in the editor.

I just know there are others out there who are experiencing the same
problem, and I would appreciate it if anyone can tell me how they
resolved the issue. Thanks in advance.

try changing the skin number

When you click on them in editor, do you get a wireframe sphere around them? Check the Fade/Dist parameters. It may be that you have the fade distance set to 1 unit accidentally or something. this has happened to me before.

Thanks. Tracer Bullet saved the day.

I even figured out the cause of the problem. When I clicked on
the model to rotate it, I accidentally clicked on the central selection
handle. And when I dragged it to reposition the model, I modified
the spherical wireframe.

To remedy the problem, open the properties dialog, and set the Min Fade
Distance to -1 and Maximum Fade Distance to 0 (for "do not fade").

For everyone reading this thread, be careful when you move and rotate
the model. You might accidentally reset the viewing
distance. To be sure that your model doesn't fade, the wireframe
surrounding the model when you select it should just be a rectangular
box. There shouldn't be any spherical wireframe at all.

That's probably the most aggravating thing about the editor. No
one in their right mind would actually set the view distance using the
spheres, yet they always get in the way when trying to move objects
(esp small ones). Hopefully in the future view distance will only
be changable in the object properties.