So after posting on gsap forums apparently the motion path plugin doesn’t really work well with three.js so i’ll leave this comment i got on gsap for anyone who has the same problem and wants an alternative solution:
The MotionPathPlugin isn’t really designed to work with three.js at the moment. That might come at later date.
Using that proxy method just isn’t going to be accurate because the plugin really only handles position and rotation in 2d.
Using constructs that three.js already provides would be a much better option.
Three.js object moving along a path / Roger Veciana i Rovira | Observable
That doesn’t mean you can’t control it with gsap. Like here, the tubePerc is being animated with gsap, which controls the movement along the path.