(GUINAME) Is not a valid member of PlayerGui error?

Whenever I try to access a child of PlayerGui ingame (in studio it works fine), it says that GUINAME is not a valid member of PlayerGui. If I use :WaitForChild, it says 'infinite yield possible'.

This is a SCRIPT located in a part in workspace. All the GUIs are valid members of PlayerGui; the script just doesn't think they are.

SCRIPT:

local part = script.Parent

--VALUES--
local shopDebounce = game:WaitForChild("ReplicatedStorage"):waitForChild("Values"):waitForChild("shopDebounce")
_G.shopBlockHitVal = false

--CAMERA--
local Camera = workspace.CurrentCamera
cameraPart = workspace.cameraPart

part.Touched:connect(function(hit)
    if  _G.shopBlockHitVal == false then
        print("no")
        wait(1)
        _G.shopBlockHitVal = true 
        print("works")
        local h = hit.parent:FindFirstChild("Humanoid")
        if h and shopDebounce.Value == false then
            print("workin'")
            shopDebounce.Value = true
            local tweenPosition = coroutine.wrap(function()
                local player = game.Players:GetPlayerFromCharacter(hit.Parent)
                player.PlayerGui.shopScreenGui:WaitForChild("mainFrame"):TweenPosition(UDim2.new(0.5, 0, 0.5, 0), "Out", "Quad", 1) --Error
            end)
            local blurEffect = coroutine.wrap(function() --blur
                print("k")
                for i = 0, 20, .25 do
                    game.Lighting.Blur.Size = i
                    wait(.1)
                end
            end)
            local cameraChange = coroutine.wrap(function()
                repeat wait()
                    Camera.CFrame = cameraPart.CFrame
                    Camera.CameraType = Enum.CameraType.Scriptable
                until Camera.CameraType ==  Enum.CameraType.Scriptable and Camera.CFrame == cameraPart.CFrame
            end)
            local fadeIn = coroutine.wrap(function()
                for i = 1, 0, -0.05 do 
                    local player = game.Players:GetPlayerFromCharacter(hit.Parent)
                    local fadeFrame = game.Players:GetPlayerFromCharacter(hit.Parent):WaitForChild("PlayerGui"):WaitForChild("fadeEffect"):WaitForChild("Frame") -- Error
                    fadeFrame.BackgroundTransparency = i
                    wait(.02)
                end 
            end)
            local fadeOut = coroutine.wrap(function()
                for i = 0, 1, 0.05 do 
                    local player = game.Players:GetPlayerFromCharacter(hit.Parent)
                    local fadeFrame = game.Players:GetPlayerFromCharacter(hit.Parent):WaitForChild("PlayerGui"):WaitForChild("fadeEffect"):WaitForChild("Frame")  -- Error
                    fadeFrame.BackgroundTransparency = i
                    wait(.02)
                end             
            end)
            fadeIn()
            blurEffect()
            wait(.75)               
            cameraChange()
            wait(2)
            fadeOut()
            wait(.1)
            tweenPosition()
        end
        wait(1)
        shopDebounce.Value = false
    end
end)

Thanks!