Hi,
the high level view is the following: when there is an update related to DNS data on an IPA server (new/updated/deleted zone, new/updated/deleted record), it gets written to LDAP. As the LDAP data is replicated to the other IPA servers, their local LDAP database gets updated.
The bind daemon running on the replica is configured with
bind-dyndb-ldap plugin, that uses the syncrepl mechanism to be warned of updates in the LDAP database. So each time there is a change in the DNS data in the LDAP server, the bind daemon is notified and can handle the change locally and update its view.
If the LDAP data is properly replicated but the bind daemon does not serve the expected records, it probably means that the syncrepl mechanism is broken. If you have a look at the journal you may see logs with "sync_repl" or "syncrepl" keywords and they will help diagnose the problem.
The bind daemon logs are located in /var/named/data/ and may also help.
flo