UI keeps leaving PlayerGui after they reset?

lplayer = game:GetService("Players").LocalPlayer

local ReachGui = Instance.new("ScreenGui")
local Button = Instance.new("TextButton")

ReachGui.Name = "ReachGUI"
ReachGui.Parent = game:GetService("CoreGui")

Button.Name = "ReachButton"
Button.Parent = ReachGui
Button.BackgroundColor3 = Color3.new(0.235294, 0.235294, 0.235294)
Button.BorderColor3 = Color3.new(0, 0, 0)
Button.Position = UDim2.new(0, 10, 0.5, 0)
Button.Size = UDim2.new(0, 100, 0, 28)
Button.Font = Enum.Font.Cartoon
Button.FontSize = Enum.FontSize.Size22
Button.Text = "Reach"
Button.TextColor3 = Color3.new(1, 1, 1)
Button.TextScaled = false
Button.TextStrokeTransparency = 1
Button.TextWrapped = false


Button.MouseButton1Click:connect(function()
    for i,v in pairs(game:GetService'Players'.LocalPlayer.Character:GetChildren())do
			if v:isA("Tool") then
				local a = Instance.new("SelectionBox",v.Handle)
				a.Adornee = v.Handle
				v.Handle.Size = Vector3.new(0.5,0.5,10)
				v.GripPos = Vector3.new(0,0,0)
				lplayer.Character.Humanoid:UnequipTools()
			end
		end
		game:GetService("StarterGui"):SetCore("SendNotification", {
		Title = "Reach applied!";
		Text = "Applied to equipped sword or clean. By Apex :)";
		})
        end)