The thin piece is actually just the angle and the archway making it thinner as its covering a bad join in the scenary 
(Although i will keep an eye on that in later testing, Thanks)
The problem you cant see because the navmesh is also displaying on the ceilings.
Just beyond the trigger box (Box with the button in it) is a door sitting in its frame with a similar archway as to the one previously mentioned.
If the Can Affect Navigation is turned on i think what is happening is that regardless of the door being opened or closed the collider for the frame blocks the navigation mesh.
With both the door and the frame having Can Affect Navigation off the navigation mesh is allowed to pass through even with the door closed.
I think the colliders will prevent enemies walking though doors they shouldnt if i make an error in their patrol routes or something.
Sssshhhhh… no one knew! 
Something that will actually be quite good fun to test 
I actually tested some today and built more level.
I was actually surprised as the AI did something rather unexpected.
I deliberatly set the Enemy AI to have a patrol point the other side of a closed door.
Expected Behaviour :- NPC to walk to door and keep trying to walk though the door.
Actual Behaviour :- NPC walks to the door, STOPS, Waits for 5 seconds (Time to wait after reaching way point) and then moves to next waypoint.
Thats some clever under the hood AI!
Ooh thats a bit sweet with out having to add anything yourself. Did it just stand their facing the door or drop.back into another state and say maybe turn around to face the other way?
What he is programmed to do via blueprint is select the waypoint, Move to it, Wait 3 seconds (+/-2), Continue to next way point.
I the video the waypoint is the other side of the door and the door can only be opened by a trigger volume on the same side as the waypoint.
Its like he tries, Realises he cant get there and goes into the wait state and then moves on!
Extremely powerful engine!
And just as a treat
WATCH AT YOUR OWN RISK 
http://sendvid.com/fm0m9oh8
Update-
Mostly working on the Dining Room and Library sections although they are far from finished a lot of work has been done with lighting.
My favourite screenshot of they day
Update Day
Been working behind the scenes a lot recently with refactoring and following Sams latest videos .
Spotted future issues in that we cant do the UI like we did in battle tank and this creates a major stumbling block at the moment. (Hopefully this will tie in with the health and damage lectures to come)
Started playing with the sequencer and made the first cut scene. (Video below)
The sequencer as yet still does not export sounds sadly and is on their to do list (Video is from in game so has sounds)
Player gets knocked out.
http://sendvid.com/fyxlm0ny
I have since got the video sequence to end at the floor and load the next level/sequence rather than respawning the player. (oops)
It is Looking very good so far @Marc_Carlyon! looking forward into playing it!
Just a question, what is knocking the player out ?
Unconscious, The player got hit in the back of the head and leaned forward, sways a bit then falls to the floor
Update
Added fade to the level sequence and destroyed the actor so gun is not appearing in the scene.
Had to set up a ResetFade level squence for the start menu to turn off the fade applied else everything is black.
That’s looking really good… definitely has the feeling of being knocked out…
Game Dev Update.
Taken a little hiatus due to kids being sick at present. (Just so you know i havent abandoned the project just delayed a bit)
Minor graphical fixes.
In the last video forgot i added placemarkers added for UI although i could do the health and damage system from this it would be blueprint and prefer to see what Sam does with it first.
Level design on hold as wondering if a transistion scene is needed to expand existing map before moving to new area. (Ie hotel rooms loaded in a level seperate rather than tagged on to the existing map.)
Will be pushing more from Tuesday onwards (Kids health depending)
I like the sound of that
I was going to say yesterday, but refrained in case I was suggesting things that were too complex, but now you’ve mentioned that… hehe… Not sure what the story is etc, but I’m guessing something along the lines of, “wake up, in a strange place, try to escape” (massively overly simplified nutshell version!)… just struck me yesterday that you video of being knocked unconscious would be quite interesting as a “how the story starts” type of video… maybe quite happily walking in some nice woodland area or whatever… here something… stop, look around… nothing… go again… hear the noise again… stop… look around… still nothing… then on the third time… thwack… fade to black… wake up in your first level
Just an idea… not really part of the game play as such but was inspired from your video content above
I think you have a pretty good read on me and game design lol.
My intentions are to expand what i have but not progress much into a new area and yes the being knocked out is the link to that.
I plan to do the transistions to the hotel rooms with puzzles to get to the final area and leave it at that as the alpha test/demo.
I am being a little tight lipped on storyline here but i have a cunning plan
Fully understand, no worries, I appreciate people don’t always like to give too much of their ideas away. Really like the sound of feel of what you are doing though, looking forwards to having a go in due course
New update video!
Bugs to fix but waiting on Sam a little here (crouch is now a pain as it broke as did the flashlight as attached to gun.)
Gun and arms can push though walls (annoying)
Aiming needs to be fixed.
Hope you enjoy what i have so far
Just wanted to update people that i havent abandoned this project but rather temporarily put it on hold.
This is due to my children being ill and myself also not being well.
When this happens its best to put things on hold until everyone is fit and well and i can devote time to coding without being bunged up myself.
I will be returning to this at some point but it may be after the christmas period now as the schools break up on friday.
I hope that that your childen gets better as soon as possible @Marc_Carlyon! Looking forward to see how Shadow Stalkers will come out to be.
Ditto what Johnny says, hope you all feel better soon and we’ll look forward to the next instalment soon