This is definitely a bug, and definitely in Skyhold - absolutely bugged by Sera's pranks, not moved somewhere else, or temporarily invisible. It has happened in both playthroughs of mine but I didn't realize why he had disappeared until the second playthrough and I finally started looking online to figure it out. All the restarts in the world won't fix it. I'm too far beyond reloading saves to get him back to talk to before the Sear pranks scene. The messenger just stands in the office completely uninteractable. Please fix this or just introduce a way to reset the messenger if it got interuppted with Seras scenes.