To everyone here, I know not all of you use the RemoveCursedWall mod, but for some reason it can invalidate NavMeshBounds in both vanilla and modded dungeons, this can cause any NPCs in said dungeons to fall through the dungeon, and if parts of the map are not loaded or in certain dungeons they will fall to the safety volume below the map and get reset to position 0,0,0. So this is literally what is happening. ( I have had confirmation that Sky Island can also cause this issue, so beware)
For those that do not use that mod, beware of any mods that edit the world as they can cause this issue depending on the way they do it.
It is always recommended to follow the guides provided by Funcom or the modding community, that was approved by Funcom, especially when it comes to things like the map.
That said, the issue may still be caused by other sources and it does not always seem to be related to one mod. I would urge Funcom to keep looking into it, as well as server owners trying to remove mods then looking for results, and if you get results from removing a specific mod, post it here so Funcom can see.