Why does this data saving/loading script work only in one game?

This script is supposed to save and load a player's data upon joining and leaving the game.

For some reason, the script works in one place, but in all the other places I've tested it in, it hasn't worked.

I've gotten this output from playing it in-game:

Argument 2 is missing or nil Stack begin Script 'ServerScriptService.data', Line 15 - upvalue LoadPlayerData Script 'ServerScriptService.data', Line 42 Stack End

Can someone please help me?

Here's the script:

local Players = game:GetService("Players")
local DataStores = game:GetService("DataStoreService")
local PlayersDataStore = DataStores:GetDataStore("Players")

local function SavePlayerData(Player)
    if Player then 
        local Leaderstats = Player:FindFirstChild("perm")
        if Leaderstats then 
            local XPValue, RankValue, HeistsValue, PrestigeValue
            XPValue = Leaderstats:FindFirstChild("XP")
            RankValue = Leaderstats:FindFirstChild("Rank")
            HeistsValue = Leaderstats:FindFirstChild("Heists")
            PrestigeValue = Leaderstats:FindFirstChild("Prestige")
            if XPValue and RankValue and HeistsValue and PrestigeValue then 
                local PlayerDS = PlayersDataStore:GetAsync(Player.UserId)
                if PlayerDS then 
                    local SavingTable = {
                        ["XP"] = XPValue.Value,
                        ["Rank"] = RankValue.Value,
                        ["Heists"] = HeistsValue.Value,
                        ["Prestige"] = PrestigeValue.Value
                    }
                    print("saved " .. Player.Name .. "'s leaderstats")
                    PlayersDataStore:SetAsync(Player.UserId, SavingTable)
                end
            end
        end
    end
end

local function LoadPlayerData(Player, XPValue, RankValue, HeistsValue, PrestigeValue)
    if Player then 
        local PlayerDS = PlayersDataStore:GetAsync(Player.UserId) -- this will return the 'SavingTable'
        if PlayerDS then 
            XPValue.Value = PlayerDS.XP
            RankValue.Value = PlayerDS.Rank
            HeistsValue.Value = PlayerDS.Heists
            PrestigeValue.Value = PlayerDS.Prestige
            print("loaded " .. Player.Name .. "'s leaderstats")
        else
            print("new player")
            PlayersDataStore:SetAsync(Player.UserId, nil)
        end
    end
end

local function SetupPlayer(Player)
    --create leaderstats folder
    local Leaderstats = Instance.new("Folder")
    Leaderstats.Name = "perm"
    Leaderstats.Parent = Player

    --create value function
    local function createNewValue(valueName)
        local newValue = Instance.new("IntValue")
        newValue.Name = valueName
        newValue.Parent = Leaderstats
        return newValue
    end

    --create values
    local XPValue, RankValue, HeistsValue, PrestigeValue

    XPValue = createNewValue("XP")
    RankValue = createNewValue("Rank")
    HeistsValue = createNewValue("Heists")
    PrestigeValue = createNewValue("Prestige")

    --load data
    LoadPlayerData(Player, XPValue, RankValue, HeistsValue, PrestigeValue)

    --autosaving
    spawn(function()
        while Player do 
            wait(10)
            if Player then 
                SavePlayerData(Player)
            end
        end
    end)
end

Players.PlayerAdded:Connect(SetupPlayer)

Players.PlayerRemoving:Connect(function(Player)
    SavePlayerData(Player)
end)