In eZ Publish 5.3 some changes have been made to the session mechanism, namely:

* Session name is now always prefixed by `eZSESSID`.

* `is_logged_in` cookie is not sent or used any more by Symfony stack (it is still used by legacy though).
  Anonymous state is now checked by the presence of a session cookie (prefixed by `eZSESSID`).

The code implementation reflects this, and in multiple places expects the session name to be prefixed this way.

However, there are multiple issues:

• The default session name for a new siteaccess is eZSESSID<siteaccess_hash>, so it won't be shared with others
• The default configuration in ezpublish.yml is 'eZSESSID' (for SAs created during setup), but this value can be modified to "whatever" (without the needed prefix)
• ezpublish.yml.example does not document this limitation, and actually uses an incorrect example:

  frontend_group:
      # Session name will be common for all siteaccesses members of this group
      # It means that session will be shared for frontend siteaccesses, but not with backoffice
      session:
          name: MyFrontendSessionName