Why is the datastore occasionally duplicating or removing items?

I made an item saving/loading script for someone recently, and it works, for the most part. Recently he told me that, though it does save the items, it occasionally duplicates them or removes them. I've tried examining it, but I can't find much of a reason for either problem.

The tools are stored in ReplicatedStorage, and copied into the player's inventory.

local PlayersItems = game:GetService("DataStoreService"):GetDataStore("Items") 

function SaveData(Player)
    local Items = {}
    for i,Item in ipairs(Player.Backpack:GetChildren()) do
        if game.ReplicatedStorage:FindFirstChild(Item.Name) ~= nil then
            if game.ReplicatedStorage[Item.Name]:IsA("Tool") then
                table.insert(Items, Item.Name)
            end
        end
    end
    PlayersItems:SetAsync(Player.UserId, Items)
end

function LoadData(Player)
    if PlayersItems:GetAsync(Player.UserId) ~= nil then
        for i,ToolName in ipairs(PlayersItems:GetAsync(Player.UserId)) do
            local Tool = game.ReplicatedStorage[ToolName]
            Tool:Clone().Parent = Player.Backpack
        end
    end
end

game.Players.PlayerAdded:connect(function(Player)

    game.Players:WaitForChild(Player.Name)
    Player:WaitForChild("Backpack")

    LoadData(Player)

    Player.CharacterAdded:connect(function()
        LoadData(Player)
    end)    

    game.Players.PlayerRemoving:connect(function(Player)
        SaveData(Player)
    end)

    Player.Backpack.ChildAdded:connect(function()
        SaveData(Player)
    end)

end)