DataStore Script Is Not Working Anymore After New Addition to Script?

As iamnoamesa has said the problem is that you are using the same data store still effectively overwriting the saved data.

There is also another issue with this design, you have now doubled the number of requests needed to save and load player data. The main point of using a table is to save more than one piece of data instead of splitting the data which requires more requests.

You can the data to the table:-

local saveData = {player.leaderstats.KOs.Value, player.Character.Volume.Value}

-- format two 
local saveData = {['ko'] = player.leaderstats.KOs.Value, ['vol'] = player.Character.Volume.Value}

If you do choose to change the save format you will need to load the data in differently. It is also a good idea to not use multiple data stores for the same game, simply change the key if you need to store data in another key as this is a more structured design.

Example not including error management:-

local DataStore = game:GetService("DataStoreService"):GetDataStore("test") -- It is best to make this something relevant to the game e.g. testingPlace1, FPS ect

-- simplify the save process
local function saveData(key, saveData)
	DataStore:SetAsync(key, saveData)
end

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

    local key = "Player_" .. player.UserId

    local plrData = DataStore:GetAsync(key)

    if plrData then -- eerror
        --Save format: {points, coins}
        player.leaderstats.KOs.Value = plrData[1] or 0
        player.Character.Volume.Value = plrData[2] or 0
    else
		--Save key: {points, coins}
		saveData(key, {player.leaderstats.KOs.Value, player.Character.Volume.Value})
    end

end)

game.Players.PlayerRemoving:connect(function(player)
	--Save key: {points, coins}
	saveData("Player_" .. player.UserId, {player.leaderstats.KOs.Value, player.Character.Volume.Value})
end)

I hope this helps, please comment if you do not understand how / why this code works.