Why are my scripts fine in studio and now when I publish my game with api services?

Pro tip:

Before I get into answering your question, I would like to say that ROBLOX studio and the real game are to different things. What I mean is that some scripts works in studio and it doesn't work on the published game.

Why is that you may ask?

This is because the two environments are not the same, one may work in one side but doesn't work on the other. Besides that, the real test is the published game.

Solution:

The cause of your error may be that the datastore itself is not working, I think that the bug was that it didn't actually save with the Player:Removing event

Since you didn't clearly, give a valid description that may not be the case.

You could try this script:

local DataStoreService = game:GetService("DataStoreService")
local Event = game:GetService("ReplicatedStorage"):WaitForChild("Events"):WaitForChild("SaveMyStats")

game.Players.PlayerAdded:Connect(function(player)
    local Stats = Instance.new("Configuration", player)
    Stats.Name = "Stats"

    -- Main stats

    local diamonds = Instance.new("IntValue", Stats)
    diamonds.Name = "Diamonds"
    diamonds.Value = DataStoreService:GetDataStore("DiamondDataStore"):GetAsync(player.UserId) or 0

    local level = Instance.new("IntValue", Stats)
    level.Name = "Level"
    level.Value = DataStoreService:GetDataStore("LevelDataStore"):GetAsync(player.UserId) or 1
    --
    -- Other stats
    local parachute  = Instance.new("StringValue", Stats)
    parachute.Name = "Parachute"
    parachute.Value = DataStoreService:GetDataStore("ParachuteDataStore"):GetAsync(player.UserId) or "Black"

    local skydiveseconds = Instance.new("IntValue", Stats)
    skydiveseconds.Name = "SkydiveSeconds"
    skydiveseconds.Value = DataStoreService:GetDataStore("SkydiveSecondsDataStore"):GetAsync(player.UserId) or 0

    local tutorial = Instance.new("BoolValue", Stats)
    tutorial.Name = "Tutorial"
    tutorial.Value = DataStoreService:GetDataStore("TutorialDataStore"):GetAsync(player.UserId) or false
    --
end)

function SaveMyStats(player)
    -- Main stats
    if player:FindFirstChild("Stats") then
        DataStoreService:GetDataStore("DiamondDataStore"):SetAsync(player.UserId, player.Stats:FindFirstChild("Diamonds").Value)
        local level = DataStoreService:GetDataStore("LevelDataStore"):GetAsync(player.UserId)
        if level ~= nil and level <= player.Stats:FindFirstChild("Level").Value then
            DataStoreService:GetDataStore("LevelDataStore"):SetAsync(player.UserId, player.Stats:FindFirstChild("Level").Value)
        elseif level == nil then
            DataStoreService:GetDataStore("LevelDataStore"):SetAsync(player.UserId, player.Stats:FindFirstChild("Level").Value)
        end
        --
        -- Other stats
        DataStoreService:GetDataStore("ParachuteDataStore"):SetAsync(player.UserId, player.Stats:FindFirstChild("Parachute").Value)
        DataStoreService:GetDataStore("SkydiveSecondsDataStore"):SetAsync(player.UserId, player.Stats:FindFirstChild("SkydiveSeconds").Value)
        DataStoreService:GetDataStore("TutorialDataStore"):SetAsync(player.UserId, player.Stats:FindFirstChild("Tutorial").Value)

    end
end

game.Players.PlayerRemoving:Connect(SaveMyStats)
Event.OnServerEvent:Connect(SaveMyStats)

If you want to change the stats just edit the leaderstats.

If you need to learn about datastore 's click here