1. Monsters can't move within 3D sectors.
2. You should make thin floors as your 3D sectors.
3. Here is your map redone as I would do it. Although, you better run when they see you.
4. I made the bar 3D sectors non-solid so everyone can shoot through them, but made the outer lines block player and monsters, so you can't go in and they can't come out.
5. Another thing, your vertices aren't aligned. If you zoom in you'll see multiple vertices real close to each other. Not good.
Edit: My response was prior to me knowing about the 3D Floor Mode in UDB. Used it for a few hours. Same things apply. You just need to make thin 3D Floors for the Monsters to stand on. If you place Monsters within the thicker 3D floors you made then they are stuck in there like it's invisible concrete. Still need to make the outer railing sectors non-solid or they will never see the Player. Make the outer ring of lines block Player and Monsters.
You do not have the required permissions to view the files attached to this post.