So I just started a classic ironman game and was doing pretty well. Then I got to an abduction mission and things were going well in the beginning. Stacked my dudes up getting ready to breach a building. Caught 3 sectoids by surprise, moved my soldiers in and killed 2 of them. One of my guys was in full cover next to a wall. Then out of the fucking blue, or out of the wall next to my guy, came 2 floaters from out of nowhere. There wasn't any darkness concealing them, there were no windows, no skylights, no second floor. Either they spawned out of nowhere, or they were outside the building and clipped through the walls. They killed 2 soldiers, one rookie and one lieutenant. I managed to complete the mission with my remaining two soldiers, luckily. But I thought what happened was just pure bullshit. It wasn't me being careless or impatient, it was just the game shitting itself and screwing me over in the process. This happened to me twice before in my normal game. A goddamn sectopod spawned out of nowhere in a small power core room in a medium sized scout UFO.
So what I want to know is,is this some kind of feature that the game failed to tell me about? That enemies can just spawn or clip through walls and floors? And has this happened to anyone else?