I can’t actually see the lead swaps in my phone but he does seem to get faster and faster over the jumps, which is a balance issue. He’s getting more and more impulsion to launch over the jumps, resulting in him getting shorter take offs.
Looked at the vids: I think this is a straightness issue on a horse who finds it easy to swap leads. First jump horse dives right as you approach, and swaps leads to accommodate, changes in the air when you try to straighten, then jumps the second part off to the right of the jump (your right), swapping again.
Pony goes off disunited, swaps in the corner (late behind) with the new change of direction, and at the next double he again dives right, gets corrected and as before, swaps leads to accommodate.
Focus on riding very straight to the center of the fence, and add poles on the ground perpendicular to the fence, or even propped on the fence, to funnel your horse to the perfect spot, nice and straight.
Use your legs and correct bend to hold the horse where you want him, on the correct lead. You can find straightening jumping exercises online too.
Seconded with @Xanthoria. After watching the video, pony looks a bit wiggly. If you are vigilant about keeping him between two legs and two hands (without bulging), I bet the swaps would reduce in frequency.
I would keep the jumps lower until you are straight as an arrow. Take your time as he may be more difficult to keep straight because he’s weak and evading.
Also, nice pony butt! Very patriotic.
I was about to say the same thing as @Xanthoria . Straightness appears to be the key factor here. I would balance back and work on the add number for straightness first and then work on the large pony number with control and straightness.