Cool picture. Now that you know how it looks, can you feel the sex doll and see if it’s a weld or a bolt? The guess is the weld at the bottom of the spine above the bolt. I have the same problem. His hips froze and tried to flex, breaking his back. I made a 1.5-inch incision in the back and found a break below the back joint. The weld is torn from an inverted U-shaped hip tube.
I would have replaced it with a T-junction made of plumbing fittings, but subsequent movements broke the weaker U-tube at the top. I tried using a thicker wire harness to fix at least the hip joint of the U-shaped tube together, and it worked a little bit, but then the lines started coming out of the tube. I did not use expansion screws. I unplugged the wires instead of piercing myself at a bad moment.
(Guess there is no really good time to pierce yourself). Therefore, I tried to cut off the broken vertices from the U-shaped tube for easy use! / 2-inch water pipe joint, L-type joint and T-type joint instead of spine instead of sex dolls beams. This size fits the tube well, but only for straight parts, so try cutting off the curve.