Having the same issue, it seems that it only happens on the first time the Run function is ran.
Edit: I looked into it more and I added a wait(1) before running the function and seems to have fixed it. Might have to do with the fact that I am creating the npc and immediately using the function. Maybe it needs to wait for everything to load?
Edit2: Pathfinding NPC Stutters for no apperant reason, after working just fine - #17 by ErwinK007
Finally found a solid solution. Need to set network ownership of the NPC to server.