What exactly do you mean by the user becomes inactive?
Are the admin/agent permissions you manually granted revoked OR are you really talking about the ACTIVE * dropdown OR even both?
Please provide a logfile that’s not out of context like above.
This error can have several sources:
your agent trying to create a new user
your admin trying to create a new user
ThirdParty authentication when you don’t automatically link an account on initial login (if the account already exist locally)
API magic you do
Normally the LDAP sync shouldn’t be affect.
Another note as I just saw it: You might want to upgrade Zammad from 2.7 to at least 2.9, as there have been fixed security issues that your installation currently doesn’t have.