working on this myself so here are some ideas... cant really say without actually seeing your form though...
from perspective of right hander, you may be straightening the rear leg when transferring weight (R->L & forward), sort of like a lunge/large step/one legged push off for horizontal jump, causing your hips to rise up/go far forward and then your upper body is straightening up as leg extends and hips come through more directly under your upper body, losing the hinge.
to solve this, need to focus on transferring weight and rotating within the hips by keeping core engaged to link legs with upper body and to stay in the hip gurdle (?) to make more body rotation rather than an exaggerated hip thrust (the thrust often is accompanied with large step or non-dominant foot - pros do it but you can see the timing of rotation/transfer and snap is there at right time rather than just lunging through the ball - a lot of these details would depend on how you are specifically executing the shot and what you are looking to do in general with the form).
to set yourself up for this, i think leg tension should be more in the inner thighs from groin to knees to engage core and allow for smooth swivel of legs during transfer and stay within hips. i am making sure to have weight on toes with foot more in line with shin and knee over foot on rear leg when loading up, if foot is too turned back or leg tension is too much focused on outside of quads, then it becomes a lunge (more similar to movements in other explosive sports rather than explosive acceleration/rotation and weight transfer).
perhaps after a shot or two you are starting to stand up, straightening the leg and your weight/balance is shifting from forward over front of foot to outside/back, becomes more of a push off.
i have been trying out the resistance band around legs to keep legs closer together (rather than sprawled out too much) so that i can rotate within my body/hips/knees better. this also helps engage the non-dominant/front leg during the backswing leading to the ready position, both knees adjust to shift weight to rear leg, core/hips engaged and using non-dominant arm to bring shoulders and upper body around enough to line up shot. the non-dominant hand movement may be affecting the axis that you are rotating on as well.
lastly, one of the youtube channels with translation mentioned that the front shoulder cant be lower than the back shoulder because then you only can rotate around the waist with that front shoulder lifting up and back shoulder swinging through (Sending ball high and to the left), whereas with rear shoulder slightly lower, can go overall forward with momentum but the shoulder and body rotation goes down to up/right to left but not sending power too far to the side/back.
regardless, to play low and to move well at the same time, requires a lot of strength & practice time in that stance, with constant reminders. can also hold onto edge of table to stay forward/low while practicing then keep same posture height (or lower) when playing further back.
