'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)