I found a problem. If the xray_config.json file specifies saving logs to files like this:

   "log": {
     "loglevel": "info",
         "access": "/var/lib/marzban-node/access.log",
         "error": "/var/lib/marzban-node/error.log"
   },

then the script does not work, it displays "There is no active user".
Right while the script was running, I deleted and added back the access and error entries, restarted Xray and the script either worked or stopped.