I was playing a Terror mission last night where after my unit would enter an area, a Cyber Disc and two Drones would come around the corner of a building. All four of my other units were in a position to shoot. My sniper with DoubleTap showed an 85% chance to hit the Cyber Disc. So I fired missing once and hitting once. My heavy missed twice, and my two assault guys hit once and missed once. I wasn't able to kill the Cyber Disc. I then reloaded from a save point and tried again, and again, and again.
Every time I got the same scenario, sniper miss, then hit. Heavy miss, miss. Assault hit, assault miss. I tried different weapon modifiers, but after five attempts I decided either the game was cheating or I was just so unlikely that given an 85% chance to hit I missed 5 / 5.