Why do I get a userId index nil error sometimes on this script?

wait(15)
local DIDend = {game.Workspace.DEndPart, game.Workspace.SEndPart, game.Workspace.TEndPart, game.Workspace.Neon1EndPart, game.Workspace.DessertEndPart,
game.Workspace.ASHEndPart, game.Workspace.BHEndPart, game.Workspace.WOEndPart, game.Workspace.DISDEndPart, game.Workspace.OREndPart, game.Workspace.CodingEnd}
local Players = game:GetService("Players")
local PlayerName = game.StarterGui.PlayerWin.Frame.PlayerName
local PlayerWinValue = game.ReplicatedStorage.EventsAndValues.PlayerWinValue
local PlayerWins = game.ReplicatedStorage.EventsAndValues.PlayerWinsValue
local Debounce = false
local Position = game.Workspace.Goto.Position

function teleport()
	local target = CFrame.new(Position)
		for i, player in ipairs(game.Players:GetChildren()) do
   			if player.Character and player.Character:FindFirstChild("HumanoidRootPart") then
      player.Character.HumanoidRootPart.CFrame = target + Vector3.new(i, i * 5, i)
  		 end
	end
end

for _,v in pairs(DIDend) do
v.Touched:Connect(function(hit)
	if not Debounce then
		Debounce = true
		local player = Players:GetPlayerFromCharacter(hit.Parent)
		if hit.Parent:FindFirstChild("Humanoid") then
			PlayerWins.Value = player.leaderstats.Wins.Value
			PlayerWinValue.Value = hit.Parent.Name
			PlayerWinValue.Value = hit.Parent.Name
			PlayerWinValue.Value = hit.Parent.Name
		end
		
	    local userId = player.UserId
		local userId = player.UserId
	    local thumbType = Enum.ThumbnailType.HeadShot
	    local thumbSize = Enum.ThumbnailSize.Size180x180
	    for i,v in pairs (game.Players:GetPlayers()) do 
        local imageLabel = v.PlayerGui.PlayerWin.Frame.PlayerAV 
        imageLabel.Image = Players:GetUserThumbnailAsync(userId, thumbType, thumbSize)		
   		 imageLabel.Size = UDim2.new(0, 180, 0, 180)
		     game.ReplicatedStorage.EventsAndValues.ShowGui:FireAllClients(game.Players:GetPlayerFromCharacter(hit.Parent))
		local player = game.Players:GetPlayerFromCharacter(hit.Parent)
    	player.leaderstats.Wins.Value = player.leaderstats.Wins.Value + 1
		player.leaderstats.Bits.Value = player.leaderstats.Bits.Value + 25
		wait(5)
		teleport()
end
wait(20)
Debounce = false

			end

sometimes It works fine sometimes I get an index userid nil error