Login is not working

Question

Recently I got in to an issue that I can't login to the system. I tried to clear the cache and reviewed all the permissions. I logged in via one time password url created by drush uli and then changed the admin password and then tried to login . Still no luck. Even when I created a new user/modified the password of existing user and tried to login, still login not working.

I tried the same scenario in an incognito window too and not working.

I have another server in the same network with the same admin and users, and with same permissions. It is working with no issues.

I had a database backup from earlier, when I restored the db first time the login is working. But then after logout it's not working.

Is it related to some caching or permission issue? If someone can give any insights it will be great.

When I checked in to the core module (user) and not getting the username in the validateName validate function , but am getting the password though. Any idea of this strange behaviour ?

in UserLoginForm.php

/**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $config = $this->config('system.site');

    // Display login form:
    $form['name'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Username'),
      '#size' => 60,
      '#maxlength' => USERNAME_MAX_LENGTH,
      '#description' => $this->t('Enter your @s username.', ['@s' => $config->get('name')]),
      '#required' => TRUE,
      '#attributes' => [
        'autocorrect' => 'none',
        'autocapitalize' => 'none',
        'spellcheck' => 'false',
        'autofocus' => 'autofocus',
      ],
    ];

    $form['pass'] = [
      '#type' => 'password',
      '#title' => $this->t('Password'),
      '#size' => 60,
      '#description' => $this->t('Enter the password that accompanies your username.'),
      '#required' => TRUE,
    ];

    $form['actions'] = ['#type' => 'actions'];
    $form['actions']['submit'] = ['#type' => 'submit', '#value' => $this->t('Log in')];

    $form['#validate'][] = '::validateName';
    $form['#validate'][] = '::validateAuthentication';
    $form['#validate'][] = '::validateFinal';

    $this->renderer->addCacheableDependency($form, $config);

    return $form;
  }

    /**
       * Sets an error if supplied username has been blocked.
       */
      public function validateName(array &$form, FormStateInterface $form_state) { 
echo $form_state->getValue('name');exit; //not getting this though
        if (!$form_state->isValueEmpty('name') && user_is_blocked($form_state->getValue('name'))) {
          // Blocked in user administration.
          $form_state->setErrorByName('name', $this->t('The username %name has not been activated or is blocked.', ['%name' => $form_state->getValue('name')]));
        }
      }