Date & Time: January 18, 10:50 PM EST
Frequency: Persistent
World name: Odin
Character name: Ehryu Raav
NPC name: Estinien
Area and coordinates: Old Sharlayan > Baldesion Annex main hall X:6.1 Y:6.2

Steps:
1. Speak with Thancred as the penultimate step in the quest "The Satrap of Radz-at-Han".
2. Enter the main hall of the Baldesion Annex.
3. Estinien is missing.

He was there, previously, and I checked that it doesn't depend on completion of the Labyrinthos route. Based on the post date of various YouTube playthroughs of this quest, he's been missing since 6.4. My screenshot first, with a YouTube screenshot included for comparison.