While creating a new user account on one my servers running FreeBSD 12, I encountered the following error:

root@nas2:~ # adduser
Username: devops
Full name: Ansible Operator  
Uid (Leave empty for default): 
Login group [devops]:      
Login group is devops. Invite devops into other groups? []: 
Login class [default]: 
Shell (sh csh tcsh nologin) [sh]: 
Home directory [/home/devops]:               
Home directory permissions (Leave empty for default): 
Use password-based authentication? [yes]: no
Lock out the account after creation? [no]: no
Username   : devops
Password   : <disabled>
Full Name  : Ansible Operator
Uid        : 1002
Class      : 
Groups     : devops 
Home       : /home/devops
Home Mode  : 
Shell      : /bin/sh
Locked     : no
OK? (yes/no): yes
pw: user 'devops' disappeared during update
adduser: ERROR: There was an error adding user (devops).
Add another user? (yes/no): no

According to a discussion on a FreeBSD forum, the problem could have caused by the databases being out of sync.

The fix was simple enough.

root@nas2:~ # /usr/sbin/pwd_mkdb -p /etc/master.passwd

root@nas2:~ # getent passwd devops
devops:*:1002:1002:Ansible Operator:/home/devops:/bin/sh