I have a terror mission where Reapers refuse to enter the Skyranger. I have 3 of them sitting before the entrance eyeing the crew hungrily. One of them eventually climbed two tiles but then turned back. At first I thought they are afraid of the reaction fire, but even with the rifles removed they are too shy to actually get to my soldiers.
I have a savegame.
The floaters in that very game behave strangely, too. I've seen one of them moving in and out of my line of vision for 5 turns straight. He just pokes his head from the corner, sees us, then dives back into cover without attempting to do anything. He has line of fire, too, because I made a reaction shot at him once.