How to get his level to increase - Encountered problem ?

I am in the process of creating a script that will allow me to make a leaderstats, as I have been good at all this time, however I am completely blocked and I would like to try to understand WHY.

When the part are equal to or greater than the value 100 I make sure that it returns to zero and that it adds a value +1 to me in my level.

However I don't understand why my code is not working on my current project.

I literally copy paste my script into another blank project and the it works, but it doesn't want to work directly in my project at all, and I have no idea.

This is my code :

local DataStoreService = game:GetService("DataStoreService")

local myDataStore = DataStoreService:GetDataStore("ScoreData")

local plr = game:GetService("Players")

local plrs = plr:GetPlayers()

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

    wait()

    local leaderstats = Instance.new("Folder")
    leaderstats.Name = "DataScore"
    leaderstats.Parent = player

    local part = Instance.new("IntValue")
    part.Name = "Part"
    part.Parent = leaderstats

    local level = Instance.new("IntValue")
    level.Name = "Level"
    level.Parent = leaderstats

    local PartData 
    local LevelData

    local success, errormessage = pcall(function()
        PartData = myDataStore:GetAsync(player.UserId.."-part")
        LevelData = myDataStore:GetAsync(player.UserId.."-level")
    end)

    if success then
        part.Value = PartData
        level.Value = LevelData
    else
        print("There was an error whilst getting your data")
        warn(errormessage)
    end

    while wait(300) do

        myDataStore:SetAsync(player.UserId.."-part", player.DataScore.Part.Value)
        myDataStore:SetAsync(player.UserId.."-level", player.DataScore.Level.Value)
        print("Data is Saved")

    end


    local checklevel = coroutine.create(function()
        while wait(1) do
            if (player.DataScore.Part.Value == 100 or player.DataScore.Part.Value >= 100) then
                player.DataScore.Part.Value = 0
                player.DataScore.Level.Value = player.DataScore.Level.Value + 1
                print("Level Up Success")
                myDataStore:SetAsync(player.UserId.."-part", player.DataScore.Part.Value)
                myDataStore:SetAsync(player.UserId.."-level", player.DataScore.Level.Value)
                print("Data is Saved")
            end
        end
    end)

    coroutine.resume(checklevel)

end)

game.Players.PlayerRemoving:Connect(function(player)
    local success, errormessage = pcall(function()
        myDataStore:SetAsync(player.UserId.."-part", player.DataScore.Part.Value)
        myDataStore:SetAsync(player.UserId.."-level", player.DataScore.Level.Value)
    end)

    if success then
        print("Player Data successfully saved!")
    else
        print("There was an error when saving data")
        warn(errormessage)
    end
end)

Where I have a problem :

    local checklevel = coroutine.create(function()
        while wait(1) do
            if (player.DataScore.Part.Value == 100 or player.DataScore.Part.Value >= 100) then
                player.DataScore.Part.Value = 0
                player.DataScore.Level.Value = player.DataScore.Level.Value + 1
                print("Level Up Success")
                myDataStore:SetAsync(player.UserId.."-part", player.DataScore.Part.Value)
                myDataStore:SetAsync(player.UserId.."-level", player.DataScore.Level.Value)
                print("Data is Saved")
            end
        end
    end)

    coroutine.resume(checklevel)

As I can see on my project it doesn't work, however when I copy paste the script like I said earlier in my posts, on another blank project the code works.

I don't understand why, yet the options for my project are good.

Other code :

    local leveling = coroutine.create(function()
        while wait(60) do
            level.Value = level.Value + 1
            character.Head.NameTag.Level.Text = "Level " .. level.Value
            DS:SetAsync(player.userId, {level.Value})
        end
    end)

    coroutine.resume(leveling)

For example on one of my other project I did this, and it worked, however I don't understand why on my project with another version it does not work.