DataStore being generally confusing. Help, anyone?

The expected result of the SaveData() function in the code below is to print "Saved data for Player1." However, it NEVER prints this. I'm having trouble because this also occurs when I replace UpdateAsync() with SetAsync(). No error is returned either.

Here's the whole script:

local DataManager = {}

local DataStoreService = game:GetService("DataStoreService")
local PlayerData = DataStoreService:GetDataStore("PlayerData")

local SessionData = {} -- Current game data
local StartingData = -- Data for players who have never played.
{
	Cash = 0, 
	Experience = 0, 
	Level = 0, 
	TotalDamage = 0, 
	EquippedWeapon = "Stick", 
	Weapons = {"Stick"}
} 

local function SaveData(Player)
	
	local PlayerId = Player.UserId
	local Data = SessionData[PlayerId]
	
	print(Player.Name .. " left. Saving data.")
	
	if Data then 
		
		local success, err = pcall(function()
			PlayerData:UpdateAsync(PlayerId, function(old) return Data end)
		end)
	
		if not success then print(err) error("Cannot save data for " .. Player.Name .. "!") end
		
	end
	
	print("Saved data for " .. Player.Name .. ".")
	
end

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

return DataManager

There is a simpler way of doing it... Here: (Hope it helps!!)

local Service = game:GetService('DataStoreService'):GetDataStore('CHANGE_THIS')--Change whats inside the '' not the variable
game.Players.PlayerAdded:connect(function(plr)
	local stats = plr:WaitForChild('leaderstats')
	local Exp = stats:WaitForChild('Exp')--Change whats inside the '' not the variable
	local Level = stats:WaitForChild('Level')--Change whats inside the '' not the variable
	local uniquekey = 'id-'..plr.userId
	local GetSaved = Service:GetAsync(uniquekey)
	if GetSaved then
		Exp.Value = GetSaved[1]
		Level.Value = GetSaved[2]
	else
		local SavingNums = {Exp.Value,Level.Value}
		Service:SetAsync(uniquekey,SavingNums)
	end
end)
game.Players.PlayerRemoving:connect(function(plr)
	local stats = plr:WaitForChild('leaderstats')
	local Exp = stats:WaitForChild('Exp')--Change whats inside the '' not the variable
	local Level = stats:WaitForChild('Level')--Change whats inside the '' not the variable
	local uniquekey = 'id-'..plr.userId
	local Savetable = {Exp.Value,Level.Value}
	Service:SetAsync(uniquekey,Savetable)
end)--Hope this helps you out!

Enjoy.