If you change the password of the admin user from the admin console without running managed servers, the managed servers cannnot boot because of an authentication error of the admin user.
Security data e.g., password) is stored in the Embedded LDAP by default and it is replicated from the admin server to the managed servers. If there is an inconsistency of the security data between the admin and managed servers, the error will occur.
In order to refresh all replicated data at boot time, you need to set 'Refresh Replica At Startup' from the Admin Console. You can set this property by following the following steps in the Admin console:
Domain --> Security --> Embedded LDAP Server.