Ok. I will get back to you in the next let's say 24 hours.
What I meant with "how big is your level" was not the actual content or size in terms of complexity but the actual quant size because it has only been thoroughly tested in the scale that you see in the demo level (or in my sidescroller where I use the pathfinding all the time and haven't had a single error since).
First guess:
Do you have multiples paths in the level which have the same name?