Leak Problems

You have a leak. Hammer is not telling you there is a leak for fun. Your map isn't sealed.

On the right side of Hammer there's a thing that says "Visgroups". Click the Auto tab, then uncheck displacements, func_details, props, and brush entities. Now is that red line going into the void?

ho ho ho holy shit dude

first thing: never func_detail a displacement, that breaks vbsp and your map wont compile

second thing: the reason i told you to turn those off is because none of them seal your map! i kinda left that part out of my post but it was heavily implied. only solid world geometry seals maps. if your floor is func_detail you may not understand the point of func_detail, read this http://www.optimization.interlopers.net/index.php?chapter=func_detail (and the rest of the guide too).

Move to World, which is right under Tie to Entity in the menu. Basically any brush that's big enough to obscure players' view of a big chunk of the map needs to be world geometry, because that's how the game avoids rendering things that wind up getting covered up.

Alternatively ctrl-shift-w to move to world. Func_detail is the default brush entity assigned when you tie to a brush (ctrl-t) and which doesn't seal, doesn't block VVIS (the process that determines visibility), is solid and casts shadows.

Correct - all exterior walls to you map need to be world brushes.

Here's a hint for quicker leak check - in the vis options panel - turn off almost everthing by unchecking

turn off

Displacements
Player clips - other tool brushes, etc,
all entities
props
func_details

Basically - what I'm getting at is, strip the map down to it's bare bones then do a compile.

If any of your outer walls are func_details you'll see a gaping hole in your map, if not and you are still getting a leak, load the pointfile and follow the line to where the leak is. If it's only 1 unit thick it's still big enough for a leak and you need to seal it.

extra:
Then once you are done that you can start to add in you area portals and then check for those leaks - those are easier to find as they are all within your world and showt you the start to finish on the same brush.

Once you have sealed your out world - check everything back on the right to bring them back into the map - then test again - if any or your entities are outside the map then you can quickly find the offending party and fix it.