UpdareGraphsNoBlock not working

I’m using a* 3.2.5 pro

I’m trying to test placement of a unit in a tower defense game, to determine if the new placement will stop to possibility of a valid path from spawn point to the player’s base.
I’m using GraphUpdateUtilities.UpdateGraphsNoBlock() as stated in the docs but it always returns true, even if I fully block the path.

I wasn’t sure that this forum was even active anymore so I’ve posted this question on the unity3d forum first (in more detail… with an image) No answers yet.
forum.unity3d.com/threads/185295-astar-project-Issue-UpdateGraphsNoBlock-not-working

Best to read details there.
Thanks