Where did XY disappear to (SI)?
SI is very plot driven, so to stop people from breaking the plot, certain NPCs stay in a unaccessible spot on the map until you meet them by following the plot, or disappear from the map until they are needed again. If you cheat by teleporting to them before the scripted meeting you are bound to break the plot and most likely forced to reload an earlier savegame or start the whole game again. So please take care when teleporting around the map.