An issue was found where a user would not be able to login via LDAP after the upgrade to V21. This has also been seen on 12.3
A forced trace would be created and the following error message could be found in the WP logs:
U00003518 UCUDB: Invalid value in Boolean field 'USR_Active'
Release : 21.0.2
Component : AUTOMATION ENGINE
The bug was found and will be fixed with V21.0.5 which is scheduled for early 2023.
As a workaround you can use LDAP Authentication via the JWP: https://docs.automic.com/documentation/WEBHELP/English/all/components/DOCU/21.0.4/Automic%20Automation%20Guides/Content/AWA/Admin/admin_LDAPConnectionSetup.htm
This is done by adding or updating the VERSION keyword to 2 in the UC_LDAP_* variable.