When fetching an entry from the ActiveDirectory server and then immediately saving it again, we see the following error:

[Symfony\Component\Ldap\Exception\LdapException]
  Could not update entry "CN=User1234,OU=Foo,OU=Users,OU=org,DC=corp,DC=domain,DC=com": Constraint violation

If using only certain attributes, e.g.

ldap_modify($this->ldap->getEntryManager()->connection->getResource(), $person->getId(), ['givenName' => 'Foo1']);

It will succeed.

So pushing the entire LDAP entry to be updated is not working or will not always work.