More or less... same salt and config.php should be actually equal in every node of a Moodle load balancing cluster plus $CFG->reverseproxy appropriate setting: you cannot easily access Moodle using more than one FQDN; it could be the reason of your Moodle session expiring due to the different cookie domain.
BTW, check the permissions and then you'll see if a new issue (FQDN) will come up.
HTH,
Matteo