why no LOGOUT event record on some OSes

Hi guys I'm new to audit, then i observed that there is no LOGOUT event record in audit.log on my ubuntu 18.04 and debian 8 OSes, while the centos7.4 and fedora33 have it. I google it but get no answer, so am I missing something about the audit rules or special audit configuration ? Below are part of records of audit in my several OSes. debian 8 lizhijian@lkp-bingo:~$ sudo aureport -e -i --summary | grep -i USER [sudo] password for lizhijian: 6  USER_START 6  USER_END 4  USER_ACCT 4  USER_CMD 2  USER_AUTH 2  USER_LOGIN ubuntu 18.04 lizj@FNSTPC:~$ sudo aureport -e -i --summary | grep USER 43241  USER_END 16946  USER_START 16718  USER_ACCT 658  USER_AUTH 543  USER_CMD 255  USER_LOGIN 9  USER_ROLE_CHANGE 5  USER_ERR 2  USER_CHAUTHTOK 1  ADD_USER fedora 33 [root@iaas-rpma linux]# aureport -e -i --summary | grep USER 7356  CRYPTO_KEY_USER 2103  USER_START 1649  USER_END 1268  USER_ACCT 1108  USER_ROLE_CHANGE 1029  USER_AUTH 895  USER_LOGIN 789  USER_LOGOUT 60  USER_CMD 14  USER_ERR 3  USER_MGMT 3  USER_CHAUTHTOK 1  ADD_USER Thanks