I've only had it happen to me when doing a repeatable in Attohwa[A] for seals. The rockhopper one, I think. But yeah, running out of range usually reloaded it. The fact a given target may be an "often used" NPC may relate to a bug with text it calls from with zone DATs. If that's the case, I'm not sure if it's even on SE's radar as I couldn't predictably replicate it.