Issue - Can't re-enable another gui

That’s quite weird. Here’s your code with some prints:

-- Required Modules
local guiSettings_Module = 
	require(game:WaitForChild("ReplicatedStorage"):WaitForChild("Modules"):FindFirstChild("Gui_Settings"));

-- My Variables.
local allPlayers = game:GetService("Players")
local localPlayer = game.Players.LocalPlayer
local playerGui = localPlayer.PlayerGui

local assetsToPreload = {workspace, playerGui}

local LoadScreen_Frame = script.Parent:FindFirstChild("Frame");
local Bar = LoadScreen_Frame:FindFirstChild("Bar");
local Inside_Bar = Bar:FindFirstChild("Inside_Bar");

-- Start loading
game:GetService("StarterGui"):SetCoreGuiEnabled(Enum.CoreGuiType.All, false)

LoadScreen_Frame.Visible = true

-- Resize to 10%
guiSettings_Module.ResizeBar(10, Inside_Bar);

-- Wait for the character to load and Resize to 40%
repeat wait() until localPlayer.Character ~= nil
guiSettings_Module.ResizeBar(40, Inside_Bar)

-- preload assets in the game
guiSettings_Module.preLoadAssets(assetsToPreload);
guiSettings_Module.ResizeBar(100, Inside_Bar);

-- Hide load screen
LoadScreen_Frame.TextLabel.Text = "LOADED!"
wait(1)

local PlayGui = localPlayer.PlayerGui:FindFirstChild("PLAY GUI")
print(PlayGui)
PlayGui.Enabled = true

game:GetService("StarterGui"):SetCoreGuiEnabled(Enum.CoreGuiType.All, true)
script.Parent:Destroy()