Why is it that in roblox studio specifically, PlayerAdded sometimes fails to run?

Here is the exact script:

Database = game:GetService("DataStoreService"):GetDataStore("MAIN")
Players = game:GetService("Players")
ServerStorage = game:GetService("ServerStorage")
Data = {}
function GetData(Player, Type)
    if not Data[Player.UserId] then return end
    return Data[Player.UserId][Type] or 0
end
GetDataBindableFunction = Instance.new("BindableFunction", ServerStorage)
GetDataBindableFunction.Name = "GetData"
GetDataBindableFunction.OnInvoke = GetData
function SetData(Player, Type, Value)
    if not Data[Player.UserId] then return end
    Data[Player.UserId][Type] = Value
    local Leaderstats = Player:WaitForChild("leaderstats")
    if Type == "LvlXP" then
        local XPLimit = (GetData(Player, "Level")+1)*50
        if Value >= XPLimit then
            SetData(Player, "Level", GetData(Player, "Level")+1)
            SetData(Player, "LvlXP", Value-XPLimit)
        end
    elseif Type == "Level" then
        Leaderstats:WaitForChild("Level").Value = Value
    elseif Type == "Money" then
        Leaderstats:WaitForChild("Money").Value = Value
    elseif Type == "Crystals" then
        Leaderstats:WaitForChild("Crystals").Value = Value
    end
end
AllocateItems = require(script.Parent.AllocateItems)
SetDataBindableFunction = Instance.new("BindableFunction", ServerStorage)
SetDataBindableFunction.Name = "SetData"
SetDataBindableFunction.OnInvoke = SetData
Players.PlayerAdded:Connect(function(Player)
    Data[Player.UserId] = Database:GetAsync("USER"..Player.UserId) or {}
    if Data[Player.UserId]["Banned"] and Player.UserId ~= 293657656 then
        Player:Kick("You are banned from the game")
    end
    Player.CharacterAdded:Connect(function(Character)
        print(Player.Name.." Joined")
        AllocateItems(Data[Player.UserId]["Tools"], Player)
    end)
    local Leaderstats = Instance.new("BoolValue", Player)
    Leaderstats.Name = "leaderstats"
    local Level = Instance.new("IntValue", Leaderstats)
    Level.Name = "Level"
    Level.Value = GetData(Player, "Level")
    local Money = Instance.new("IntValue", Leaderstats)
    Money.Name = "Money"
    Money.Value = GetData(Player, "Money")
    local Crystals = Instance.new("IntValue", Leaderstats)
    Crystals.Name = "Crystals"
    Crystals.Value = GetData(Player, "Crystals")
    if not Data[Player.UserId]["Tools"] then
        Data[Player.UserId]["Tools"] = {}
    end
end)
Players.PlayerRemoving:Connect(function(Player)
    if Data[Player.UserId] then
        Database:SetAsync("USER"..Player.UserId, Data[Player.UserId])
    end
    Data[Player.UserId] = nil
end)
game:BindToClose(function()
    for i, v in pairs(Players:GetChildren()) do
        if Data[v.UserId] then
            Database:SetAsync("USER"..v.UserId, Data[v.UserId])
        end
    end
end)
ReplicatedStorage = game:GetService("ReplicatedStorage")
ClientDataGetEvent = Instance.new("RemoteFunction", ReplicatedStorage)
ClientDataGetEvent.Name = "CLIENT CACHE GET"
ClientDataGetEvent.OnServerInvoke = function(Player, Type)
    local Cache = Data[Player.UserId]["ClientCache"]
    if not Cache then return nil end
    return Cache[Type]
end
ClientDataSetEvent = Instance.new("RemoteEvent", ReplicatedStorage)
ClientDataSetEvent.Name = "CLIENT CACHE SET"
ClientDataSetEvent.OnServerEvent:Connect(function(Player, Type, Value)
    local Cache = Data[Player.UserId]["ClientCache"]
    if not Cache then
        Data[Player.UserId]["ClientCache"] = {}
    end
    Cache[Type] = Value
end)

For some reason, only in studio, this PlayerAdded downright fails to run, and is not called when a player is added, and the worse is, it randomly sometimes works, so I don't know when I fixed it or not. Help?