why does my python tkinter gui close after I spam the back button?

The problem with my code is that when I click on the back button which is the top left button, it goes back to the main screen and then I click on the register button which takes me to the register screen, it is fine and if I clikc the back button again, the GUI would close automally with nothing said in the terminal.

This is the register page with the back button

import sqlite3
from tkinter import *
from tkinter import messagebox  # Import messagebox for error messages
import re  # Import re module for regular expressions
import customtkinter
from PIL import ImageTk, Image
# Destroy this window and open the login screen
def login():
register_screen.destroy()
import login  # Assuming there is a login.py file to open the login screen
def main():
register_screen.destroy()
import main
def register_user():
# Get username and password
username_value = username.get()
password_value = password.get()
# Check password requirements
# Check if there is at least one capital letter in the password section
if not re.search(r"[A-Z]", password_value):
error_label.config(text="Password must contain at least one capital letter", fg="red")
return
# Check if there is at least one number in the password section
if not re.search(r"\d", password_value):
error_label.config(text="Password must contain at least one number", fg="red")
return
# Check if there is at least one symbol in the password section
if not re.search(r"\W", password_value):
error_label.config(text="Password must contain at least one symbol", fg="red")
return
# Insert the user into the database
cursor.execute("INSERT INTO users (username, password) VALUES (?, ?)", (username_value, password_value))
connection.commit()
login()
# Designing for registration
register_screen = tk.Tk()
register_screen.title("Register")
register_screen.geometry("500x800")
register_screen.resizable(width=False, height=False)
# Create a database connection
connection = sqlite3.connect("db/registration.db")
cursor = connection.cursor()
# Create a table for registration
cursor.execute("CREATE TABLE IF NOT EXISTS users (id INTEGER PRIMARY KEY AUTOINCREMENT, username TEXT, password TEXT)")
# Background image
background_image_login = PhotoImage(file="assets/background2.png")
background_label_login = Label(register_screen, image=background_image_login)
background_label_login.place(x=0, y=0, relwidth=1, relheight=1)
# Creating an empty tuple for username and password
username = StringVar()
password = StringVar()
# Create an empty label for the image
logo = ImageTk.PhotoImage(Image.open("assets/Logo.png").resize((180, 130), Image.ANTIALIAS))
logo1 = customtkinter.CTkButton(master=register_screen, image=logo, text="", compound="left", hover=False, bg_color="#020202")
logo1.place(relx=0.48, rely=0.2, anchor=CENTER)
# Create an empty label for the text
username_label = Label(register_screen, text="Username")
username_label.place(relx=0.5, rely=0.3, anchor=CENTER)
# Create a customentry widget for username
username_entry = customtkinter.CTkEntry(master=register_screen, textvariable=username, placeholder_text="Username", height=35, width=250)
username_entry.place(relx=0.5, rely=0.35, anchor=CENTER)
# Create an empty label for the text
password_label = Label(register_screen, text="Password")
password_label.place(relx=0.5, rely=0.4, anchor=CENTER)
# Create a customentry widget for password
password_entry = customtkinter.CTkEntry(master=register_screen, textvariable=password, placeholder_text="Password", height=35, width=250, show="*")
password_entry.place(relx=0.5, rely=0.45, anchor=CENTER)
# Create a button
register_button = customtkinter.CTkButton(master=register_screen, text="Register", command=register_user, height=35, width=250)
register_button.place(relx=0.5, rely=0.55, anchor=CENTER)
# Create an empty label for the error message
error_label = Label(register_screen, text="", fg="red")
error_label.place(relx=0.5, rely=0.62, anchor=CENTER)
arrow_image = ImageTk.PhotoImage(Image.open("assets/hi.png").resize((50, 50), Image.ANTIALIAS))
arrow_button = customtkinter.CTkButton(master= register_screen,image = arrow_image,text="", compound="left" ,fg_color='black', hover_color='black', command= main) 
arrow_button.place(relx=0.1 , rely = 0.1, anchor = CENTER)
register_screen.mainloop()
# Close the database connection
connection.close() 

This is the home page code

import tkinter
from tkinter import *
import os
import customtkinter
from PIL import ImageTk, Image
root = Tk()
# Designing the main screen
def main_screen():
root.geometry("500x800")
main_frame = Frame(root,bg ='#020202')
main_frame.pack(padx=20)
main_frame.pack()
background_image = PhotoImage(file="assets/Aim high.png")
background_label = Label(root,image = background_image)
background_label.place(x=0, y=0, relwidth = 1 , relheight = 1)
root.title("Account Login")
top_text=Label(root,text="Welcome to FitQuest",bg="#020202",font=("Calibri", 45))
top_text.pack(pady=0, anchor =tkinter.CENTER)
def register():
root.destroy()
import register
def login():
root.destroy()
import login
#Login button 
Login_button = customtkinter.CTkButton(master=root, text="Login", command=login, height = 35, width = 250,bg_color="#020202")
Login_button.place(relx=0.48, rely=0.3, anchor=tkinter.CENTER)
#register button
register_button = customtkinter.CTkButton(master=root, text="Register", command=register,height = 35, width = 250, bg_color="#020202" )
register_button.place(relx=0.48, rely=0.4, anchor=tkinter.CENTER)
#Logo act as a button 
logo = ImageTk.PhotoImage(Image.open("assets/Logo.png"),Image.ANTIALIAS)
button1 =customtkinter.CTkButton(master=root,image=logo,text="",compound="left" , hover=False, bg_color="#020202")
button1.place(relx=0.48, rely=0.158, anchor=tkinter.CENTER)
root.mainloop()
main_screen() 

An import statement does not have to re-execute the module contents, and in your case that's exactly what happens. Modules in Python are cached in sys.modules, and every import statement checks against that cache first to determine if the module is already loaded, and if it is, the cached module object is returned.

Instead of destroying screens and reimporting modules, just put the initialization and deconstruction code inside functions, import modules unconditionally, and then call the functions when necessary