How can my script not find my PlayerGui when its there from the start?

I have a frame in a screenGui named "OreBar" in StarterGui, and when I try to access the frame with my script, I cannot find it. This is the error on line 4

It works in studio but NOT the game The script is not in screenGui, but it does access it.

The following script goes into workspace.ores:

function AddOre(player) --this goes in ore
	local ClickedOre = script.Parent
	local OreValue = ClickedOre.V.Value
	player.PlayerGui:WaitForChild("OreBar", 20) --NOT WORKING HELP
	local OreBar = player.PlayerGui.OreBar.Frame

	local CurrentOreSpot = nil
	for i=1,6,1 do
		if OreBar["Ore"..i].Text == "None" then
			CurrentOreSpot = OreBar["Ore"..i]
			break
		end
	end
	
	if CurrentOreSpot == nil then
		print("No more room!")
		return
	end
	
	ClickedOre.Position = Vector3.new(190, 100, -375)
	ClickedOre.Anchored = true
	CurrentOreSpot.Text = "This ore is $"..OreValue
	CurrentOreSpot.Ore.Value = ClickedOre
	
end

script.Parent.ClickDetector.MouseClick:connect(AddOre)

You can safely ignore ALL the CurrentOreSpot junk, it is just part of the things inside OreBar

Without the time parameter in line 4 I get error: Infinite yield possible for WaitForChild()

With it I get error after 10 seconds: cannot find OreBar in PlayerGui. It is there. Ive made sure while playing the game in studio. This is the only script of 3 total scripts that modifiy OreBar, another being a script inside OreBar, and another is the intro to the game. None modify Name property of OreBar.

You say it's in screengui, if so it has to be a local script. Yet you have

The problem here is you need instead of:

script.Parent.ClickDetector.MouseClick:connect(AddOre)

which is meant for world objects in workspace. Gui's work differently which require MouseButton1Up, MouseButton1Down, MouseButton1Click, MouseButton2Down, MouseButton2Up, and MouseButton2Click, it should be:

script.Parent.MouseButton1Click:connect(AddOre)