Infinite Yield on WaitForChild even though the child is right there?

Hello, I have been recently trying to code a script that simply removes I gui that a :insert script creates abruptly in my game. I cannot understand this issue clearly.

My code:

local players = game:GetService("Players")
player = players.LocalPlayer


players.PlayerAdded:Connect(function(player)
	wait(1)
	if player ~= nil then
	local a = player:FindFirstChild("PlayerGui")
	local b = a:WaitForChild("MuteButtonGui") -- Infinite yield, look at screenshot though!
	b.Enabled = false
	end
end)

https://imgur.com/a/yuBcjLn

This is most likely I simply issue I cannot wrap my head around haha!