How can I stop these joints from breaking?

My problem is essentially this

wait()
Wave = 1

print("Wave Loaded")
function Create(item, amount, Xran1, Xran2, Zran1, Zran2, CPart, WaitTime)
    for i = 1, amount do
        if item then
            local Creation = game.ServerStorage.Instances[item]
			wait()
            local Instance = Creation:Clone() 
			wait()              
            Instance.Parent = game.Workspace.GameHolder
			wait()
            local xpos = math.random(Xran1, Xran2)           
            local zpos = math.random(Zran1, Zran2)           
            Instance[CPart].CFrame = CFrame.new(xpos,4,zpos)
			wait(0.05)
            wait(WaitTime)
        else
            print("Item is nil")                
        end
    end
end

whenever I use this function (It's for a modular wave script) the NPC's spawned have about an 85% chance of having all their joints broken, and I have no idea why. I've tried putting "Instance:MakeJoint()" after every single step, but it only made the problem worse. Any suggestions?

If it helps, this never happened before today, maybe a roblox update broke it... Edit: This also doesn't happen in offline Test mode, only when online does it happen