Why does my script not know what HumanoidRootPart is? The script tells it what it is

I'm making a game for fun and I'm coding the MainFramework but with teleporting it says Attempted to index with a nil value:WaitForChild(), Can anyone help me?

Here's the code:

local EventsModule = require(script:WaitForChild("EventsModule"))
local MethodNames = {}

for MethodName, Method in pairs(EventsModule) do
	if type(Method) == "function" then
		table.insert(MethodNames, MethodName)
	end
end

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local Remotes = ReplicatedStorage:WaitForChild("Remotes")

local Values = ReplicatedStorage:WaitForChild("Values")
local Status = Values:WaitForChild("Status")

local timeBetweenEvents = 5
local AllPlates = ReplicatedStorage:WaitForChild("Plates"):GetChildren()

local minimumPlayers = 0

while true do
	Status.Value = "Waiting for enough players!"
	
	repeat wait(1) until game.Players.NumPlayers >= 1
	
	Status.Value = "Intermission"
	
	local Plates = ReplicatedStorage.Plates:Clone()
	Plates.Parent = workspace
	
	local Players = game.Players:GetPlayers()
	local PlayersAlive = {}
	local PlatesAlive = {}
	
	for i, player in pairs(game.Players:GetPlayers()) do
		local plate = Plates:FindFirstChild("Plates"..i)
		local character = player.Character
		
		local HumanoidRootPart = character:WaitForChild("HumanoidRootPart")
		if HumanoidRootPart and #Players >= minimumPlayers then
			HumanoidRootPart.CFrame = plate.CFrame * CFrame.new(0,3,0)
			player.serverData.playerPlate.Value = i
			
			local plateOwner = Instance.new("StringValue")
			plateOwner.Name = "plateOwner"
			plateOwner.Value = player.Name
			plateOwner.Parent = plate
			
			table.insert(PlayersAlive, player)
			table.insert(PlatesAlive, plate)
			for i, v in pairs(PlayersAlive) do print(i,v) end
			
			character.Humanoid.Died:Connect(function()
				print(player.Name.." has died")
				
				table.remove(PlayersAlive, table.find(PlayersAlive, player))
				table.remove(PlatesAlive, table.find(PlatesAlive, plate))
			end)
		end
	end
	
	for i, plate in pairs(Plates:GetChildren()) do
		local plateOwner = plate:FindFirstChild("plateOwner")
		if plateOwner.Value == nil then
			plate:Destroy()
		end
	end
	
	while #PlayersAlive > 0 do
		wait(timeBetweenEvents)
		
		local RandomMethodName = MethodNames[math.random(1, #MethodNames)]
		local Method = EventsModule(RandomMethodName)
		Method()
	end
	
	Plates:Destroy()
end

Sounds like the script is running before each player has fully loaded. I've written an example on what happens when a player joins and when their character loads. The script(s) add the new player to a global table and waits till their character loads before returning the character in a Global table.

Caller Script:

local PlayersGroup = game:GetService("Players")
local SSS = game:GetService("ServerScriptService")
local PlayersMod = require(SSS:WaitForChild("Players Module"))

PlayersGroup.PlayerAdded:connect(function(plr) PlayersMod:addPlayer(plr) end)

while true do
	local Players = PlayersMod:getPlayers()
	for k,plr in pairs(Players) do
		print(k, ".Character = ",plr.Character)
	end 
	wait()
end

And the module script:

local plrs = {
	Players = {}
}

function plrs:addPlayer(plr)
	self.Players[plr] = {
		Character = nil
	}
	while plr.Character == nil do wait() end -- wait for the character to load before continuing!
	plrs.Players[plr].Character = plr.Character -- Set this players table entry to their character model
end

function plrs:removePlayer(plr)
	if(self.Players[plr] == nil) then
		warn(tostring(plr).." is not part of the players table!") 
	else
		plrs.Players[plr] = nil
	end
end
function plrs:getPlayers()
	return plrs.Players
end

function plrs:getPlayer(plr)
	if(self.Players[plr] == nil) then
		warn(tostring(plr).." is not part of the players table!") 
	else
		return plrs.Players[plr]
	end
end

return plrs

The module script is kinda a hacked together thing, but it works as an example.

The only two function i've tested is getPlayers() and addPlayer() the other two should work, but they are untested and might need a little work.

hope this helps!