What I see is a person who continually drives with their seat and who is constantly behind the motion. Yet, when the horse approaches the jump, they seem to be simply a passenger. There is little communication evident between horse and rider. Stay more forward, soften your seat and balance the horse better. Through leg and half halts, you can balance the horse, improve the impulsion and engage the haunch.
These are the tools the horse needs to jump better. You have a lovely horse who seems to have a good attitude towards jumping. The rider is just not living up to her part of the partnership, in my opinion.
BTW, one word that can improve the partnership........dressage!!
Your horse is nice mover. I think your horse was way too out of control and he started getting flat over the jumps and he seems like he does not listen to you at all.
The reason your horse stopped at the one jump was because you "threw" him away right before the take off. If you notice you leaned forward too soon. If you look at the second time you got over it, because you sat and waited.
You obviously know what you're doing, so Im guessing you were just having an off day. It happens.