Why Does Parts not Change size In Workspace?

So i Wanted to Recreate one of my old projects. Its a Music Visualizer. You Put a song and then it will make a visulazion of it. Now, It only runs When i press "run". But when i hit play and Join the game it just dont moves at all. this is the script:

script.Parent.Sound:Play() -- Sound

while true do
	vol = script.Parent.Sound.PlaybackLoudness 
	script.Parent.Part1.Size = Vector3.new(0.5,vol/math.random(30,50),0.5) -- The math.random is used so it Looks like a real visualizer or stuff
	script.Parent.Part2.Size = Vector3.new(0.5,vol/math.random(30,40),0.5)
	script.Parent.Part3.Size = Vector3.new(0.5,vol/math.random(30,50),0.5)
	script.Parent.Part4.Size = Vector3.new(0.5,vol/math.random(30,50),0.5)
	wait()
end

Now theres no errors in the Output and Its A serverscript.

anyone help?

It happened to me while I was making NPC Pathfinding and during 'Run", it worked fine and when I used to join, it stuttered a lot. I fixed that issue by setting Network Ownership to the server.

Assuming, Part1, Part2, Part3 and Part4 in a model. You can add in the script:

script.Parent.PrimaryPart:SetNetworkOwner(nil)

Make sure to set PrimaryPart to the model.

Lemme know if it helps!