When a player touches the box spawn in the picture, the approaching zombies derp and stand still, if the player moves away, the zombies will keep following you again, but if you stay there, the zombies stay stood still until they are either pushed by other zombies or killed.
Ive no idea whats causing this, playable area is there, so is zone, im not sure there are any dodgy clips or anything

Do you have pathnodes there? Did you check with dev 1 and ai_shownodes 1 on to see if the paths are connected there?

Sorted it, it was because the pathnodes were in the box, rather than ending before it. removing them fixed it, thanks for suggesting pathnodes anyway