How do I get my proposed terrain to show up in the same view window as my cross section and my vertical alignment?

My regular terrain isn't showing up on my cross section either. I had this same problem yesterday, and I was able to fix it by using the "process corridor" button. Somehow that change didn't save?  I guess I must have accidentally freed the file instead of checking it in. It's weird because last time my terrain wasn't showing up on my vertical alignment or my cross section, and today it's just my cross section. Anyway, I tried the "process corridor" button today and it didn't work. The terrain is definitely set to active, though.

Yes, the terrain should be attached to the 3D view. ORD can generally manage it from there.
Since a terrain is a 3D element in a 3D file, it needs to be referenced to the Default-3D model.
At least, that's my understanding.

It doesn't look like there's anything in my 3D file, which is weird because the references are referenced in and turned on. It's not usually like this. This is seems like a weird problem.

And I have no idea why, but every time I go from my 3D model to my Default model, all of the view windows except view 1 and view 2 (which shows up blank) vanish, and I have to set up the views again.

That looks like that Default-3D model is attached twice. Since that's the reference dialog, you don't have two models with the same name, you have one model attached two times.