Ваша JavaScript функция щелчка неверна.
Используйте приведенный ниже синтаксис javascript
executor.executeScript("arguments[0].click();", WebElement);
Ниже код работает для меня:
Actions builder = new Actions(driver);
Action mouseOverMenu;
mouseOverMenu = builder.moveToElement(driver.findElement(By.id("ui-id-2"))).build();
mouseOverMenu.perform(); //accessing Enabled menu option
WebDriverWait wait = new WebDriverWait(driver, 30);
wait.until(ExpectedConditions.visibilityOfElementLocated(By.id("ui-id-4")));
wait.until(ExpectedConditions.elementToBeClickable(By.id("ui-id-4")));
mouseOverMenu = builder.moveToElement(driver.findElement(By.id("ui-id-4"))).build();
mouseOverMenu.perform(); //accessing Downloads submenu option
WebElement webElement2= driver.findElement(By.cssSelector("a#ui-id-6.ui-corner-all")); // #ui-id-6 is for pdf, #ui-id-7 csv so on
JavascriptExecutor executor = (JavascriptExecutor)driver;
executor.executeScript("arguments[0].click();", webElement2);