WeldConstraint position goes wild

I want to make the weldconstraint position stay where it is, and not happen like in the video.

as you can see below the problem is that the position of the part connected to the humanoid looks like the part replaces the position of the Humanoidrootpart: here is the footage:
I feel is like the part becomes an anchor even though I have disabled it

image image when the code cloned a part/executed: image

any help? i already used normal weld and didnt go well