Robotframework tests fails when run multiple suites together but pass when run individual suites

I have a directory Robot and have multiple suites (.robot files) in it. When i run individual file, tests run successfully. but when i run all suites together, the first .robot file run properly but from second file i get No keyword with name ‘Open New Browser’ found.
command to run all suites under a folder:
PycharmProjects/{projectname}/venv/bin/python -m robot -d Results --loglevel DEBUG -e EXCLUDED -i OUStests /Users/{user}/PycharmProjects/{projectname}/Tests/Web/Robot

I use robot framework with combination of python and selenium.

these are my test setup and tear down:

Test Setup run keywords Open New Browser
Test Teardown run keywords Close All Browsers

my custom keywords file:

from SeleniumLibrary import *
from …webdriver import WebDriver
from robot.libraries.BuiltIn import BuiltIn

class CommonKeywords(SeleniumLibrary):
def open_new_browser(self, alias=None):
self.register_driver(WebDriver().driver, alias=alias)

def close_all_browsers(self):

my file:

from selenium.webdriver import DesiredCapabilities
from .configuration import *
from selenium import webdriver
from robot.libraries.BuiltIn import BuiltIn
from selenium.webdriver.remote.command import Command
from urllib3.exceptions import MaxRetryError

class WebDriver:
def __get_driver(self):
# Get to see if already a driver:
driver = BuiltIn().get_variable_value(’${driver}’, None)
if driver is None:
return None
return driver
except MaxRetryError:
return None

def __init__(self, name=None, version=None):
    driver = self.__get_driver()
    if driver is None:
        self.__headless = None
        self.__local = None = name
        self.conf = get_configuration('Browser')
        driver_path = self.conf.get('driver_path', 'Resources/chromedriver')'From My WebDriver')
        from selenium.webdriver import ChromeOptions
        options = ChromeOptions()
        caps = DesiredCapabilities.CHROME
        caps['goog:loggingPrefs'] = {'performance': 'ALL'}
        if self.headless:

        if self.local:
            driver = webdriver.Chrome('Resources/chromedriver', chrome_options=options, desired_capabilities=caps)
            driver = webdriver.Remote(command_executor="http://chrome:4444/wd/hub", options=options)

        driver.set_window_size(1920, 1080)
        self.driver = driver
        BuiltIn().set_global_variable('${driver}', driver)
        self.driver = driver

def close(self):
    """Closes all open browsers and resets the browser cache.

            After this keyword new indexes returned from `Open Browser` keyword
            are reset to 1.

            This keyword should be used in test or suite teardown to make sure
            all browsers are closed.
    BuiltIn().set_global_variable('${driver}', None)