Hey, what a cool horse! I would like to see a more solid lower leg to give you a better base of support. It slides back at various times during your round and is detracting from a good 2 point position. Also, keeping your toes forward will help anchor your heel at the girth.
One other thing and this is my opinion only, I would lose the spurs for a while. It seems that you are unintentionally using them (due to the lower leg position and angle of your toes) at times which is resulting in a very forward horse, too forward at times for a nice clean jump. Because he is so forward you are compensating by holding him back even harder. I feel this may have contributed to the stop that you had at jump 4. Your horse is being told to go forward but being blocked by your hands and then uncertain as to whether to approach the jump or not so he stops. Just my observation.
If it were me, I would not worry about the spurs for a while, just use the crop and only use it when you need. Give him more freedom to move with your hands and practice your release, especially for a class of this height.
One other thing - your horses technique is lacking. Please don't be offended by this but he is lunging over the jumps, his knees are very untidy and his center of balance is off. I would recommend lots of gymnastic excercises to brush up his technique and get him jumping cleanly and accurately before I did too many height classes.