I think that it is best that you look directly on our Live Level, its code is : 0875-2415-4249
As soon as you see the walkers in game they will be spawned but not moving.
I will try to make the video as well and send it.
Like I said before, I suspect issue is present because Nav Mesh is not generated on the whole Landscape area, which I figured out by using Nav Mesh debug mode.
And why Nav Mesh is not generating, that is the real question.