'attempt to index a nil value'?

Hello! I'm building an Obby right now and it took me a long time to find a working stage and leaderboard script. I managed to find one but it seems to only work some of the time*... I keep getting two errors, but in this question I will only ask for help on one... might as well focus on them one at a time!

*as in it will sometimes work perfectly for all tests and then just seem to break at a random moment...

The full error is:

17:18:23.779 - Workspace.Checkpoints.ChangeUserStageOnTouch:10: attempt to index a nil value

The file throwing the error is a normal script file:

local x=script.Parent:GetChildren()

for i=1,#x do
    if x[i]:IsA("BasePart") then
        if tonumber(x[i].Name) then
            local Num=tonumber(x[i].Name)
            x[i].Touched:connect(function(hit)
                local player = game.Players:GetPlayerFromCharacter(hit.Parent)
                if player then
                    if player:WaitForChild("leaderstats",1):WaitForChild("Stage",1).Value == (Num - 1) then
                        if hit.Parent.Humanoid.Health ~= 0 then
                            player.leaderstats.Stage.Value = Num
                        end 
                    end 
                end 
            end)
        end
    end
end

I know line 10 is the issue but as I haven't scripted using Roblox before I'm not sure how to fix it...

I read something on here regarding a similar problem but I couldn't see how I would solve this for myself... thanks for any help! I feel I will be asking a few questions here haha.

EDIT: Added the leaderboard script -

DS1=game:GetService("DataStoreService"):GetDataStore("STAGE_1")

game.Players.PlayerRemoving:connect(function(Player)
    DS1:SetAsync(Player.UserId,Player.leaderstats.Stage.Value)
end)

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

    local Folder = Instance.new("Folder")
    Folder.Name = "leaderstats"

    local Stage = Instance.new("IntValue")
    Stage.Name = "Stage"
    if DS1:GetAsync(Player.UserId) then
        Stage.Value = DS1:GetAsync(Player.UserId)
    else
        Stage.Value = 1
    end
    Stage.Parent = Folder
    Folder.Parent = Player


    Player.CharacterAdded:Connect(function() -- The function object or character property of the player DON'T WORK for line 29! WTF! So line 25 + line  29 work fine.
        local Character=workspace:WaitForChild(Player.Name,5)
        local x=workspace:WaitForChild("Checkpoints",5):FindFirstChild(Player:WaitForChild("leaderstats",5):WaitForChild("Stage",5).Value)
        if x then
            if game.Players:GetPlayerFromCharacter(Character) then
                Character:MoveTo(x.Position)
            end
            print("Found matching stage: ".. tostring(x) ..". Moving [".. string.upper(Character.Name) .."] to (".. tostring(x.Position) ..").")
        end
    end)

    Player:LoadCharacter()

end)