Visportal keeps getting dropped?

[Uncertain Title]

I have a small room that I split almost completely in half using a "wall" (brush). I cloned a wall of the sealing brush and dragged it to the small opening, cut a hole into it, and turned it into a visportal. Yet for some reason, the portal gets dropped at runtime.

It's puzzled me for the past couple hours, and I can't quite understand why it won't work.

Here is a rough picture of what I am trying to make. The red lines are entryways, while the pink is the portal I am trying to make.

 

[geegee]

The entryways need visportals too, else it's still just one area. 

[thebigh]

Take a look at your lin file in DarkRadiant and follow the red zigzagging line.

Basically, if it's possible to go through your visportal, loop back around, and pass through it again without ever having to go through another visportal, it will drop. In this schematic, black is worldspawn brushes, green is a visportal, and red is the .lin file. To avoid looping back through the visportal, I needed to put an additional portal in one, or both, of the other entranceways.

 

 

Another very common cause of visportal drops is if there is a gap between your worldspawn and portal. In that case the lin file will look like a tiny red loop or splotch at the portal.

[stgatilov]

In the recent TDM, any dropped portal should result in some kind of warning during dmap.
Find this warning, and if a .lin file is generated, inspect it in DarkRadiant.

Most likely it will solve your problem.

[Uncertain Title]

Thank you all for the tips, they all helped me narrow down the issue. Turns out I had accidentally adjusted some walls and it caused the visleafs to not be completely separated from each other.