Password expiration is configured for 90 days by default. This was introduced in NSX-T 2.4.0 due to security requirements.
NSX-T 2.4.0 Password Policy Enhancements enforce a minimum password length of 12 characters for default passwords. It also introduces the ability to set password expiration times and generates alarms when the password is about to expire.
For more details, please refer to VMware NSX-T Data Center 2.4 Release Notes.
For more information, refer to this VMware Knowledge Article: https://kb.vmware.com/s/article/70691
Note: Please be aware that this issue can also impact Pivotal Application Service (PAS) when used in conjunction with NSX-T. The symptoms will be slightly different but the resolution is the same.