Invisivble strip gets rendered over solid geometry

[The Asylum]

That just magically started appearing during testing, and nothing ive done so far has gotten it to render properly. The other side of the wall looks fine, but this strip just won't render properly. There's another wall on the other side of the camera, and that's got no problem rendering either. Even installing old geometry from the previous build won't get this strip to render properly.

Ideas?

 

[spruce]

Have you seen "check for problems" in Hammer? does compile fire any specific errors? is there any particular error in console? is there a brush clipping into/near this strip?

 

[The Asylum]

Nope, nope, and nope.

Oddly enough though, once I intentionally put the floor brush through the wall, it rendered fine. Have no idea why, but I'm not gonna argue with the results.