Data Store Script Doesn't Save Value?

When I test my script in studio, there are no errors in the output. The value gets updated in a different script, and the value is changed in the server but the value doesn't save. How could I fix this?

Script:

local Data = game:GetService('DataStoreService'):GetDataStore('DataStore')
local prefix = 'user_'
local StartingWorld = game:GetService("ReplicatedFirst").WorldStorage:FindFirstChild("TestPlaceFolder")

game.Players.PlayerAdded:connect(function(player)
    local PlayerWorldID = Instance.new('StringValue',player)
    PlayerWorldID.Name = 'PlayerWorldID'
    local plrData = Data:GetAsync(prefix  .. tostring(player.UserId))

    if plrData then
          PlayerWorldID.Value = plrData[1]
   else

  PlayerWorldID.Value = StartingWorld.Name

    Data:SetAsync(prefix  .. tostring(player.UserId), {
        PlayerWorldID.Value,
     })
   end

end)

game.Players.PlayerRemoving:connect(function(player)
    Data:SetAsync(prefix  .. tostring(player.UserId), {
        player.PlayerWorldID.Value,
    })
end)