selenium move_to_element does not always mouse-hover

You need to do this step by step checking the visibility of the elements you are going to interact with using Explicit Waits, do not use time.sleep() - it is not reliable and error-prone:

from selenium import webdriverfrom selenium.webdriver.common.action_chains import ActionChainsfrom selenium.webdriver.common.by import Byfrom selenium.webdriver.support.ui import WebDriverWaitfrom selenium.webdriver.support import expected_conditions as ECdriver = webdriver.Chrome()driver.get("http://www.flipkart.com/watches/pr?p%5B%5D=facets.ideal_for%255B%255D%3DMen&p%5B%5D=sort%3Dpopularity&sid=r18&facetOrder%5B%5D=ideal_for&otracker=ch_vn_watches_men_nav_catergorylinks_0_AllBrands")driver.maximize_window()# wait for Men menu to appear, then hover itmen_menu = WebDriverWait(driver, 10).until(EC.visibility_of_element_located((By.XPATH, "//a[@data-tracking-id='men']")))ActionChains(driver).move_to_element(men_menu).perform()# wait for Fastrack menu item to appear, then click itfastrack = WebDriverWait(driver, 10).until(EC.visibility_of_element_located((By.XPATH, "//a[@data-tracking-id='0_Fastrack']")))fastrack.click()