Some of the angles make it difficult but I think there is a general pattern, I’ve posted screenshots in a few posts due to 500kb attachment restriction, they do tell a story when compared side by side.
In the second video there is a tendency on the second rep especially to sit back further with a less upright torso, and the result is more hip extension relative to knee extension, with knee extension leading hip extension on the concentric and the hips rising early i.e. less smooth co-ordination of these two actions. The right elbow also appears to drift further away from the line of the body than the left elbow.
In the second video during the early concentric of the second rep (first rep as well to a lesser degree) I see:
1. Subtle weight shift to right leg- hips move laterally slightly.
2. Right knee comes in during sticking point at start of concentric.
3. Twitch at SIJ/hip with femur internal rotation- Watch thigh/glute/low back around belt level on right side.
4. Stumble off right leg at completion of rep as the above rotation compromises balance.
Generally posture in 237X2 is sitting back much more in a power squat style, if you view frame by frame it’s pretty clear– > poorer co-ordination of knee and hip extension. At the end of the eccentric, it’s likely the femur glides down slightly with anterior tilt to assist stability due to the power squat posture, changing the line of force application slightly and pushing the COM forward a little more rather than up at the start of the concentric.
The seemingly higher right elbow makes sense in the context of these as does the external rotation of the right foot, which seems to be greater than the left.
While light isn’t great if you keep an eye on the right femur throughout and pause between 0:04-0:05 after you have stood up and as you step away afterwards, the right foot seems more externally rotated and moreover there is some evidence of a “winking patella” due to an internally rotated femur relative to foot/ankle alignment. Like this but obviously less severe:
The right shoulder appears lower as well, which combined with the weight shift to the right in the squats may suggest leg length discrepancy. This kind of structural abnormality would definitely fit with the shifts in the squat video above. It doesn’t seem to be too evident in the 235X2 video, though the angle is not perpendicular and no view of the right leg, posture is clearly taller and overall the movement is much smoother.
A weight shift to the right may indicate a leg length dicrepancy (right shorter). It may be worth getting a therapist to look at leg length discrepancy, femur rotation/alignment for right vs left, and a comparison of ankle mobility and single leg squat for right vs left. In terms of training I’d focus on controlling the SIJ/femur with a slower eccentric for all squatting exercises and be careful of asymmetric catches on olympic lifts. I’d Potentially re-examine your technique on piriformis and hip flexor stretching, making sure lumbopelvic alignment is sound as per my post elsewhere.
There is a trend as you increase weight to a less upright power squat style, which to some extent will occur naturally. 210X5 below is very upright compared to both 235X2 and 237X2, still a little pelvic tilt as you come up on reps 3-4, but rep 5 shows very good stability through the sticking point. As far as possible I’d avoid power squat form and put a premium on SIJ stability and co-ordination of hip and knee movement. In the the 237X2 video the co-ordination is lost slightly and the logical compensations mentioned above seem to be occuring. I wouldn’t rule out the belt playing a role as well in terms of losing some impetus for active stabilisation of the SIJ.