I had this problem as well. The only workaround i could find was changing your language at the game launcher to japanese, for some reason that made the quest npcs reappear. I'm finding the problem becoming more frequent in more story quests as i progress. Very frustrating having to log out and change the language all the time.

I've also noticed that a lot of sidequests have Japanese titles, Azys La being the worst place were every sidequest has japanese titles