TSRW mesh disappearing?

Hello lovely people! Not sure if this is the right place to ask, feel free point me somewhere else. 

I wanted to convert a lovely curved staircase from The Sims 2 to 3. Opened it in SimPe, got the mesh, textures, all good. Fixed it up in Milkshape, exported as a TSRW (WSO) object. 

I was going to use a deco statue or something as a base, and replace it with my mesh (not trying to make it functional). 

But the problem: when I open it in TSRW, the mesh for the steps is gone. I can see the shadow of it, like, it’s there. But it’s not there. It doesn’t seem like a texture thing, I’ve tried that. I’ve tried to fix it for hours but I can’t seem to figure out what the problem is. Maybe it’s super obvious. 

Any help would be appreciated!