bug wih LookAt?,is there bug with .LookAt method?

lookat worked well for the original object, but by copying the object or a prefab from the object using it, the new instance will follow the target indeed, but seem not stable, chacking , trembling…
,i build a script that make a “canon” following an gameobject.
il worked perfectly, the gameobject is public, so i put the player . and the canon follow the player .
but if i copy paste the canon, or if i create a prefab with the canon, then, the second canon or more in the scene is chaking. still following but chacking, trembling, it is not stable.
the tricky thing, if cretae a new player and replace the ancient player with the new one on each canon, there will not chack anymore and all work perfectly.
but again, by creationg a new one frome prefab or copy paste, and put the actual player as the target from the public field, the bug reaper again… what is going on?

one of the reason i found was the target, it seem to pass threw a sleep state or awake state continuously. that was the cause of the trembling. that does not explain why duplicate the canon, using the script made some of them working well, and other not working…
a solution is to put the target rigidbody in sleep state in the update() . and all the canon stop chacking. at least.