You’re right. Every time a new ticket is created by a customer there is a log entry:
[19-Nov-2020 08:29:25 UTC] PHP Warning: session_regenerate_id(): Cannot regenerate session id - session is not active in /www/htdocs/w0140e5e/osticket/open.php on line 49
In vanilla osTicket or Chrome you just dont see the error, because everything seems to work fine.