Zombies/Hordes Phase through walls In this specific circumstance

[Auklin]

Video demonstrating the bug down below. If you create OR destroy a 'wall' above an existing barrier, the barrier logic appears to assume that the wall must have been altered. Allowing hordes to path-find through.

It appears once you reload the chunk, it will close off the wall again, but if you altered the wall before this, it assumes there is a hole. 

How I discovered this bug:
I build that bridge across and sheet roped down.

I shot, climbed back up, shot some more, ran out of ammo.

drove to the gun store, got more ammo, came back, and the horde phased through that brick wall.