This was an interesting issue I encountered on a Linux machine. I renamed a user in /etc/passwd, but forgot to rename its entry in /etc/shadow.
The result was that every login attempt ended up logging the following and immediately closing the SSH connection for the user.
sshd[22715]: fatal: Access denied for user username by PAM account configuration [preauth] sshd[22723]: fatal: Access denied for user username by PAM account configuration [preauth] sshd[23144]: fatal: Access denied for user username by PAM account configuration [preauth]
So a reminder to myself: if you rename a user in /etc/passwd, also rename it in /etc/shadow.
If you encounter this error too, check if the user that’s trying to log in has a shadow-entry. It doesn’t need a password, but it needs a corresponding entry in /etc/shadow.