When the Ender Dragon dies and shoots out beams of light, its green hitbox shown with F3+B will glitch out rapidly.

The body part hitboxes do not move with the ender dragon in its death animation, unlike the main hitbox.

While an ender dragon is dying, the main hitbox properly moves with the ender dragon into the sky.
This is not the case for the hitboxes for the body parts, which stay in place the moment its death animation begins, and vanish when the animation ends.