locating element explicitly waiting and without wait what's difference?

The question is about selenium webdriver’s explicitly wait feature which is same locating action with a timeout. Webdriver waits element to be visible or present. In my situation, I locate elements with explicit waiting and without it. When it is without the explicit wait, it founds and assigns it. But below, I also try to locate element explicitly waiting, that variable is unassigned, and in such form passes to for iteration, and my for iteration gives UnboundLocalError
I know that error is not selenium but python based. I can get rid of that error by using instead of pass y_priceNewProds = x_priceNewProds` but I need to understand why selenium webdriver cannot locate the element with wait if it already a line above found it. There must be cookies also.

code is below;

import pandas as pd
from selenium.webdriver.chrome.service import Service
from selenium.webdriver.chrome.options import Options
from selenium import webdriver
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.common.by import By

#reading from csv file url-s
def readCSV(path_csv):
    df=pd.read_csv(path_csv)
    return df

fileCSV=readCSV(r'C:UsersAdminDownloadsurls.csv')
length_of_column_urls=fileCSV['linkamazon'].last_valid_index()

def create_driver():
    chrome_options = Options()
    chrome_options.headless = True
    chrome_options.add_argument("start-maximized")
    # options.add_experimental_option("detach", True)
    chrome_options.add_argument("--no-sandbox")
    chrome_options.add_experimental_option("excludeSwitches", ["enable-automation"])
    chrome_options.add_experimental_option('excludeSwitches', ['enable-logging'])
    chrome_options.add_experimental_option('useAutomationExtension', False)
    chrome_options.add_argument('--disable-blink-features=AutomationControlled')

    webdriver_service = Service(r'C:pythonProw_crawlAmznScrpBotchromedriver.exe')
    driver = webdriver.Chrome(service=webdriver_service, options=chrome_options)

    return driver

#going to urls 1-by-1
def goToUrl_Se(driver):
    global counter
    counter = 0
    for i in range(0, length_of_column_urls + 1):
        xUrl = fileCSV.iloc[i, 1]
        print(xUrl,i)
        # going to url(amazn) via Selenium WebDriver
        driver.get(xUrl)
        parse_data()
        counter+=1
    driver.quit()

#fetch-parse the data from url page
def parse_data():
    global asin, title, bookform, priceNewProd
    wait=WebDriverWait(driver,timeout=20)

    try:
        #trying code snippets where locating elements occur by XPATH, in some ofthem
        #there is also WebDriver explicit wait, that element has both methods
        #with presence_of element wait method and without explicit wait method. Just trying to understand
        #why sometimes elements cannot be located on page
        y_data_index=wait.until(EC.presence_of_element_located((By.XPATH,"//div[@data-index='1']")))
        print(y_data_index.text,'y_index')
        x_data_index=wait.until(EC.visibility_of_element_located((By.XPATH,"//div[@data-index='1']")))
        print(x_data_index.text,'x_index')
        x_titles=driver.find_elements(By.XPATH,'//span[contains(@class,"a-size-medium")]')
        x_bookforms = driver.find_elements(By.XPATH,'//div[contains(@class,"a-section a-spacing-none a-spacing-top-micro s-price-instructions-style")]//div[contains(@class,"a-row a-size-base a-color-base")]//a[contains(@class,"a-size-base a-link-normal puis-medium-weight-text s-underline-text s-underline-link-text s-link-style s-link-centralized-style a-text-bold")]')
        x_priceNewProds = driver.find_elements(By.XPATH,'//div[contains(@class,"a-row a-size-base a-color-base")]//span[contains(@data-a-color,"base")]//span[contains(@class,"a-offscreen")][1]')
        y_priceNewProds=wait.until(EC.visibility_of_all_elements_located((By.XPATH,'//div[contains(@class,"a-row a-size-base a-color-base")]//span[contains(@data-a-color,"base")]//span[contains(@class,"a-offscreen")][1]')))
    except:
        pass

    for i in range(len(x_titles)):
        x_title=x_titles[i].text
        x_priceNewProd = x_priceNewProds[i].text
        print(x_priceNewProd)
        y_priceNewProd=y_priceNewProds[i].text
        print(y_priceNewProd)
        try:
            x_bookform=x_bookforms[i].text
            print(x_bookform)
        except:
            x_bookform='-'
        title = x_title
        bookform = x_bookform
        priceNewProd = x_priceNewProd
        write_to_csv()

def write_to_csv():
    if counter==0:
        df=pd.DataFrame({'Products':title,'Bookform':bookform,'Price':priceNewProd},index=[0])
        wr=df.to_csv('results_new00.csv',index=False,mode='w')
    else:
        df=pd.DataFrame({'Products':title,'Bookform':bookform,'Price':priceNewProd},index=[0])
        wr=df.to_csv('results_new00.csv',index=False,mode='a',header=False)

driver=create_driver()
goToUrl_Se(driver)

y_priceNewProd=y_priceNewProds[i].text UnboundLocalError: local variable 'y_priceNewProds' referenced before assignment