Issue with NPC sync distance?

[Cubical]

I'm having a strange issue where if I log on in a level all NPCs act fine but if I login on a different level and then walk over to some NPCs they aren't visible until very close. I've included a video below. Does anyone know the root cause of this? It only seems to happen to certain ones while others are always fine.

edit: ignore the music, i didn't know it would add it.