As many others have said, you are "jumping ahead" of the horse. You need to sit back, and wait for the horse to start to lift off the ground before you go into your two point. Jumping ahead can result in getting popped out of the saddle since you are throwing your weight at the horse prematurely. The horse is not at the highest point of the jump, yet you are at the lowest point of your two point. Therefore, the horse's upward motion is throwing you up and back, especially as it reaches the top of the jump. Because you are thrown back at the highest point of the jump, you continue to fall backwards as the horse descends, making you fall even further behind. You appeared to be looking down at the jumps in several of the videos. Looking down only encourages you to jump ahead. I would pick a point just above eye level as you approach a jump. Do not take your eyes off of the point until you have landed. This will help you sit up more during the approach, take off, and landing. Also, grab the horse's mane on your take off until you begin to get a feel for when to time your two point. Hope that helps! :)
Strength is not defined by physical ability. It is determined by your actions and the compassion of your soul.