Host registration or subscription-manager refresh command failed with "400 - Bad Request" after upgrade to Red Hat Satellite 6.8.5

Issue

• Registering new host or subscription manager refresh command fails with "400 - Bad Request" after upgrade to Satellite 6.8.5.

    [root@rhel7-vm:~]#subscription-manager register --activationkey RHEL7 --org Example_Org
    The system has been registered with ID: 70620e3d-07dd-454a-8341-3b03468ad049
    The registered system name is: rhel7-vm
    Network error. Please check the connection details, or see /var/log/rhsm/rhsm.log for more information.
  
    [root@rhel8-client:~]#subscription-manager refresh
    Network error. Please check the connection details, or see /var/log/rhsm/rhsm.log for more information.
    [root@rhel8-client:~]#
    [root@rhel8-client:~]#cat /var/log/rhsm/rhsm.log
    2021-04-15 02:10:09,203 [ERROR] subscription-manager:922948:MainThread @managercli.py:218 - Unable to perform refresh due to the following exception: HTTP error (400 - Bad Request)
    2021-04-15 02:10:09,203 [ERROR] subscription-manager:922948:MainThread @managercli.py:219 - HTTP error (400 - Bad Request)
    Traceback (most recent call last):
      File "/usr/lib64/python3.6/site-packages/subscription_manager/managercli.py", line 1058, in _do_command
        self.entcertlib.update()
      File "/usr/lib64/python3.6/site-packages/subscription_manager/certlib.py", line 32, in update
        self.report = self.locker.run(self._do_update)
      File "/usr/lib64/python3.6/site-packages/subscription_manager/certlib.py", line 18, in run
        return action()
      File "/usr/lib64/python3.6/site-packages/subscription_manager/entcertlib.py", line 42, in _do_update
        return action.perform()
      File "/usr/lib64/python3.6/site-packages/subscription_manager/entcertlib.py", line 119, in perform
        expected = self._get_expected_serials()
      File "/usr/lib64/python3.6/site-packages/subscription_manager/entcertlib.py", line 292, in _get_expected_serials
        exp = self.get_certificate_serials_list()
      File "/usr/lib64/python3.6/site-packages/subscription_manager/entcertlib.py", line 272, in get_certificate_serials_list
        reply = self.uep.getCertificateSerials(identity.uuid)
      File "/usr/lib64/python3.6/site-packages/rhsm/connection.py", line 1340, in getCertificateSerials
        return self.conn.request_get(method)
      File "/usr/lib64/python3.6/site-packages/rhsm/connection.py", line 880, in request_get
        return self._request("GET", method, headers=headers, cert_key_pairs=cert_key_pairs)
      File "/usr/lib64/python3.6/site-packages/rhsm/connection.py", line 906, in _request
        info=info, headers=headers, cert_key_pairs=cert_key_pairs)
      File "/usr/lib64/python3.6/site-packages/rhsm/connection.py", line 765, in _request
        self.validateResponse(result, request_type, handler)
      File "/usr/lib64/python3.6/site-packages/rhsm/connection.py", line 863, in validateResponse
        raise NetworkException(response['status'])
    rhsm.connection.NetworkException: HTTP error (400 - Bad Request)