Ah, I see.
What happens is that an AI issues a path request, then the AI is deactivated, a few frames later when the path request is completed, the AI is inactive and thus, the coroutine cannot be started. You can solve this by, at the start of the OnPathComplete function add something like:
if (!this.active) return;
I think the AIPath script can handle starting to search for paths again when becoming active again, but you might want to check that to make sure.