Yup its all because you moved only cube. End point (or start point) of physics constraint stayed in beginning location. You need to update also that point.
But there is one big problem with constarints they do horrible things to physics, when your cube collides while being limited (at exactly moment you limit its movement), other objects warp trough space. I wish epic cleared constrains (or made good tutorial about how to use them).
I had your warping problem with asteroids coming to planet orbit. Never really could solve it. Temporary hack was to calculate asteroid impact location, spawn that asteroid at exactly that location (together with constrain), then move asteroid to starting location and push towards impact location. When asteroid was at that location I turned on constraint. No warping.
I tried multiple times but I could not make it work. I could not create constrain in realtime that had beginning and end point at locations i desired, and that constrained my asteroid to orbit.
Later on we found out that gameplay on planets orbit is quite limiting us with level design, and this boring to player.