Lets be clear about this. When you do not enable your obstacle avoidance, it is OFF. Yes, even on a waypoint mission. This isn't the first time the matter has come up here. Sometimes when you plan a waypoint mission and then go out and fly it, you have neglected to survey the site and have unintentionally instructed your drone to fly into an obstacle. If you fly the mission without obstacle avoidance turned on, you are essentially instructing your drone to crash into whatever you failed to understand is in the way. It is just following your instructions. You are darn lucky to still have your drone intact.