What do I do when I exceed maximum recursion depth in __instancecheck__ in python pong?

I created pong with the help of a youtube tutorial https://www.youtube.com/watch?v=XGf2GcyHPhc&ab_channel=freeCodeCamp.org , and everything works, except the ball goes really fast, and then really slow and so on. The speed of the ball is inconsistent and this makes it hard to play. I did some research and found this, How to fix inconsistent frame rate (speed) in python turtle , I think I did what I had to do, but now the program runs for a couple of seconds, and then stops and gives this error: RecursionError: maximum recursion depth exceeded in instancecheck , what do I do?
This is my code right now:

import turtle

window = turtle.Screen()
window.title("Pong by @Ubevg")
window.bgcolor("black")
window.setup(width=800, height=600)
window.tracer(0)

# score
score_A = 0
score_B = 0

# paddle A
paddle_A = turtle.Turtle()
paddle_A.speed(0)
paddle_A.shape("square")
paddle_A.shapesize(stretch_wid=5, stretch_len=1)
paddle_A.color("white")
paddle_A.penup()
paddle_A.goto(-350, 0)

# paddle B
paddle_B = turtle.Turtle()
paddle_B.speed(0)
paddle_B.shape("square")
paddle_B.shapesize(stretch_wid=5, stretch_len=1)
paddle_B.color("white")
paddle_B.penup()
paddle_B.goto(350, 0)

# ball
ball = turtle.Turtle()
ball.speed(0)
ball.shape("square")
ball.color("white")
ball.penup()
ball.goto(0, 0)
ball.dx = 0.5
ball.dy = 0.5

# pen
pen = turtle.Turtle()
pen.speed(0)
pen.color("white")
pen.penup()
pen.hideturtle()
pen.goto(0, 260)
pen.write("Player A: " + str(score_A) + "  " + "Player B: " + str(score_B), align="center", font=("Courier", 24, "normal"))

# function
def paddle_A_up():
    y = paddle_A.ycor()
    y += 20
    paddle_A.sety(y)

def paddle_A_down():
    y = paddle_A.ycor()
    y -= 20
    paddle_A.sety(y)

def paddle_B_up():
    y = paddle_B.ycor()
    y += 20
    paddle_B.sety(y)

def paddle_B_down():
    y = paddle_B.ycor()
    y -= 20
    paddle_B.sety(y)

# keybind
window.listen()

window.onkeypress(paddle_A_up, ("w"))
window.onkeypress(paddle_A_down, ("s"))

window.onkeypress(paddle_B_up, ("Up"))
window.onkeypress(paddle_B_down, ("Down"))


# main game loop
def move_balls():
    global score_A, score_B
    window.update()

    # move the ball
    ball.setx(ball.xcor() + ball.dx)
    ball.sety(ball.ycor() + ball.dy)

    # border checking
    if ball.ycor() > 290:
        ball.sety(290)
        ball.dy *= -1
    elif ball.ycor() < -290:
        ball.sety(-290)
        ball.dy *= -1

    if ball.xcor() > 390:
        ball.goto(0, 0)
        ball.dx *= -1
        score_A += 1
        pen.clear()
        pen.write("Player A: " + str(score_A) + "  " + "Player B: " + str(score_B), align="center",
                  font=("Courier", 24, "normal"))
    elif ball.xcor() < -390:
        ball.goto(0, 0)
        ball.dx *= -1
        score_B += 1
        pen.clear()
        pen.write("Player A: " + str(score_A) + "  " + "Player B: " + str(score_B), align="center",
                  font=("Courier", 24, "normal"))

    # paddle and ball collisions
    if ball.xcor() > 340 and ball.xcor() < 350 and (ball.ycor() < paddle_B.ycor() + 40 and ball.ycor() > paddle_B.ycor() -40):
        ball.setx(340)
        ball.dx *= -1

    elif ball.xcor() < -340 and ball.xcor() > -350 and (ball.ycor() < paddle_A.ycor() + 40 and ball.ycor() > paddle_A.ycor() -40):
        ball.setx(-340)
        ball.dx *= -1

    window.ontimer(move_balls(), 100)

move_balls()