It seems like a network ownership issue, but the parts are created locally and so that shouldn’t be an issue?
You cannot set the NetworkOwnership of client sided parts anyway since they are not visible on the server. If the part was on the server I would understand why the freezing was happening but I have no clue why it happens when everything is client-sided.
My apologizes, I realize that now. Is it absolutely necessary that you create the part on the client? If not, could you do something like making it only visible for certain clients? Unfortunately I am pretty sure if the part is created on the client and the part is not within the simulation radius of the client then nothing is simulating the physics (nil).