At least I'm pretty sure it's a bug.
I'm in that house that has all the traps and Lava in one room in the SE section of the main map. The Lava room has a Chest in the corner and so I teleported one my guys over to open the chest. Now he's stuck because it says target out of sight, so I can't target him to teleport him back across the Lava. I also got that when I tried to teleport the chest. But nothing is obstructing my view and I was able to teleport my guy there but now I can't teleport him back. Sometimes that happens elsewhere too. Objects in plain sight with no walls or rocks or trees in the way and it will say Target out of sight.