I've seen this happen to a team member. There are some issues sometimes when players fall to the void and they swim in the underground lake that the whole island rests on. He probably was under you laughing the whole time. (my team member was the one that fell into the lake in another game and there was another guy from another team swimming with him)
I was able to shoot a guy with my VSS through a wall because he was proning behind it and his knee and foot was visible, and hittable as well. I'm pretty sure this is a known bug, but just putting it out there in case there isn't enough feedback on this.