I noticed this (might be) a known issue where other people’s characters sometimes go into de-sync mode and do not appear correctly.
And, while I definitely think it’s not an easy fix I might find some resemblance or at least why it happens. When player A talks to any NPC, (sometimes) their character gets bugged out, and other players see player A standing in 1 spot despite his/her pets moving around correctly (Deathstalker or Blade Spirits for example).
I really don’t know how deep of root the problem is but it indeed is very annoying to experience from time to time, maybe you guys can check that area out.
There is always been a temporary workaround like others have said in the past (teleporting to different zone and back) but that’s really nifty so to say.