During a vassal attack on SirLach's Red Rocket, I killed all the defenders, but still had two quest markers there like two non-hostile enemies (green), both at parking lot level. I toggled collisions and looked underneath, but nothing. I waited a long time, but no indication that I had taken control. I tried again from before I scheduled the attack, and the only difference was that one of the two markers was at second floor level inside. Third try, same result. It wasn't a prebuild, so I can destroy it and try another plan, but I figured it might be worth reporting.