My weld module keeps bugging, please provide information ?

local module = {}

function WeldParts(parts)
local prev
    for i = 1,#parts do 
    if (parts[i]:IsA("BasePart")) then 
        if (prev ~= nil)then 
            local weld = Instance.new("Weld") 
            weld.Part0 = prev 
            weld.Part1 = parts[i] 
            weld.C0 = prev.CFrame:inverse() 
            weld.C1 = parts[i].CFrame:inverse() 
            weld.Parent = prev 
        end 
        prev = parts[i] 
    end 
end
end


function module:FormWeldToChar(char, pos, model)
    local ready = false
    local posp = nil

    local forweldparts = {}

    for _, v in pairs(char:GetDescendants()) do
        if v.Name == pos and v:IsA("BasePart") then
            ready = true
            posp = v
        end
    end
    if ready == true then
        posp.Anchored = true
        wait()
        model:SetPrimaryPartCFrame(posp.CFrame)
        for _, d in pairs(model:GetDescendants()) do
            if d:IsA("BasePart") and d.Name ~= "tref" then
                table.insert(forweldparts, d)
                table.insert(forweldparts, posp)
            end
        end
        wait()
        WeldParts(forweldparts)
        for i = 1, #forweldparts do
            forweldparts[i].Parent = char
        end
        wait()
        model:Destroy()
        for i = 1, #forweldparts do
            forweldparts[i].Anchored = false
        end
    end
end

return module

that is the module, it works fine in small games, however when in large games it bugs out and the offset of the weld gets messed up, the module is called like so;

Module:FormWeldToChar(CHAR, "Torso", Model_Clone)

I would like help revising this module so the offset of the model-parts don't get messed up when welded, all the parts of the model clone are positioned and the "tref" functions as a canvas for easy-placement.