Leaderboard stops working once in game?

When I test with the play button on studio it works perfectly fine! However, when I go to the play the game on a server it doesn't work. There's absolutely no errors in output. It's located in workspace and is a normal script.

function onXPChanged(player, XP, level)
    if XP.Value>=level.Value * 10 then -- Lv 1 to Lv 2 need 20 XP 

        level.Value = level.Value + 1 
    end
end

function onLevelUp(player, XP, level)
    print('nothing')
end


function onPlayerRespawned(player)
    wait(5)

    player.Character.Humanoid.Health = player.Character.Humanoid.Health + player.leaderstats.Level * 10

    player.Character.Humanoid.MaxHealth = player.Character.Humanoid.MaxHealth + player.leaderstats.Level * 10

end

function onPlayerEntered(newPlayer)

    local stats = Instance.new("IntValue")
    stats.Name = "leaderstats"


   local kills = Instance.new("IntValue")
    kills.Name = "Kills"
    kills.Value = 0

    local deaths = Instance.new("IntValue")
    deaths.Name = "Deaths"
    deaths.Value = 0

   local level = Instance.new("IntValue")
   level.Name = "Level" -- The Name of LV
   level.Value = 1

   local xp = Instance.new("IntValue")
   xp.Name = "XP" -- The Name of XP
   xp.Value = 0

    stats.Parent = newPlayer
    kills.Parent = stats
    deaths.Parent = stats
   level.Parent = stats
   xp.Parent = stats

    xp.Changed:connect(function() onXPChanged(newPlayer, xp, level) end)
    level.Changed:connect(function() onLevelUp(newPlayer, xp, level) end)

    while true do
        if newPlayer.Character ~= nil then break end
        wait(5)
    end

    local humanoid = newPlayer.Character.Humanoid

    humanoid.Died:connect(function() onHumanoidDied(humanoid, newPlayer) end )

    -- start to listen for new humanoid
    newPlayer.Changed:connect(function(property) onPlayerRespawn(property, newPlayer) end )


    stats.Parent = newPlayer

end

function Send_DB_Event_Died(victim, killer)
    -- killer may be nil
    local killername = "unknown"
    if killer ~= nil then killername = killer.Name end
    print(victim.Name, " was killed by ", killername)

    if shared["deaths"] ~= nil then 
        shared["deaths"](victim, killer)
        print("Death event sent.")
    end
end

function Send_DB_Event_Kill(killer, victim)
    print(killer.Name, " killed ", victim.Name)
    if shared["kills"] ~= nil then 
        shared["kills"](killer, victim)
        print("Kill event sent.")
    end
end



function onHumanoidDied(humanoid, player)
    local stats = player:findFirstChild("leaderstats")
    if stats ~= nil then
        local deaths = stats:findFirstChild("Deaths")
        deaths.Value = deaths.Value + 1

        -- do short dance to try and find the killer

        local killer = getKillerOfHumanoidIfStillInGame(humanoid)


        Send_DB_Event_Died(player, killer)
        handleKillCount(humanoid, player)
    end
end

function onPlayerRespawn(property, player)
    -- need to connect to new humanoid

    if property == "Character" and player.Character ~= nil then
        local humanoid = player.Character.Humanoid
            local p = player
            local h = humanoid
            humanoid.Died:connect(function() onHumanoidDied(h, p) end )
    end
end

function getKillerOfHumanoidIfStillInGame(humanoid)
    -- returns the player object that killed this humanoid
    -- returns nil if the killer is no longer in the game

    -- check for kill tag on humanoid - may be more than one - todo: deal with this
    local tag = humanoid:findFirstChild("creator")

    -- find player with name on tag
    if tag ~= nil then

        local killer = tag.Value
        if killer.Parent ~= nil then -- killer still in game
            return killer
        end
    end

    return nil
end

function handleKillCount(humanoid, player)
    local killer = getKillerOfHumanoidIfStillInGame(humanoid)
    if killer ~= nil then
        local stats = killer:findFirstChild("leaderstats")
        if stats ~= nil then
            local kills = stats:findFirstChild("Kills")
         local xp = stats:findFirstChild("XP")
            if killer ~= player then
                kills.Value = kills.Value + 1
            xp.Value = xp.Value + 3

            else
                kills.Value = kills.Value - 0

            end
            Send_DB_Event_Kill(killer, player)
        end
    end
end

game.Players.ChildAdded:connect(onPlayerEntered)