PrestaShop - Cannot login to back-office after upgrade (1.7.2.0 -> 1.7.7.4)

I have upgraded PrestaShop on my local machine (Xampp, PHP 7.4, MariaDB 10.1.22) according to official PrestaShop devdocs: https://devdocs.prestashop.com/1.7/basics/keeping-up-to-date/upgrade/

In front-office, everything seems to be okay. The problem I am facing is I cannot login into back-office now. After filling up correct email and pwd and click login button, it doesn't show any message and just reloads the page. If I fill up incorrect email or pwd, there is common error "The employee does not exist, or the password provided is incorrect."

I have also tried to login via incognito mode in Chrome, Opera or Firefox, but in each case the result is the same - reloading the login page.

PrestaShop domains in table ps_shop_url are ok. Variables PS_SHOP_DOMAIN_SSL and PS_SHOP_DOMAIN in ps_configuration seems to be ok too. I have also cleared the cache dirs (ps_root/var/cache, ps_root/cache, ps_root/app/cache) but again with no result.

Please, anyone could help?

Thank you very much

EDIT: After some debugging I found out what may causing this problem: In AdminControllerCore@init method, there is some employee checking at line 2804 ( !$this->context->employee->isLoggedBack() ), and this function checks validity of logged employee in back-office. However the employee id is null and it seems the id is not loaded from cookie... but I dont know why...

EDIT 2: Finally, there is a problem with validating cookie-checksum in method Cookie@update at these lines:

        /* Check if cookie has not been modified */
        if (!isset($this->_content['checksum']) || $this->_content['checksum'] != $checksum) {
            $this->logout();
        }

The checksums are not the same. Hence it logs me out everytime... Anyone knows what is this behavior caused by? I can just comment the logout line out and it works, but I understand that is not proper solution and may be a security risk...

Thanks!