In the screenshots below you can see a rock that is missing a collision box, in this match someone was sniping with a .50 cal down the 'alley' just outside C on Push hidden behind the rock texture with the barrel peeking out - near impossible to see unless you sneak up and hear the .50 cal blowing from that direction...
Screenshot 1 shows me aiming at the rock in question and screenshot 2 shows its location on the map.

Screenshot 1
Screenshot 2