Interesting. I made the path much smaller along the spiral staircase.
Now when my player triggers the c_scan(), I get the same pop-up error I mentioned before, and the monster warps from where I put it a little ways up on the spiral staircase, to the beginning node of the path at the bottom of the spiral staircase. This time, the monster is not coming from underneath the floor, but simply starts at the beginning node of the spiral staircase path, on top of the floor.
The monster then moves up the spiral staircase with no walking animation, even though I put the animation there. It just moves up the staircase path motionless.