Problem with master-slaves synchronisation

Hello I have a big problem with syncronisation between some openldap slaves and the openldap Master.

In fact, i have a network of openldap slaves (8) and an openldap master who send all the information to the slaves. Actually when i add a new openldap slave, i get the old information from the master but for all the newest one, i dont have synchronisation.

i have openldap 2.3.43 installed on the openldap Master openldap 2.3.3 installed on the openldap slaves. DB4.2-util installed on both openldap master and openldap slaves.

What can be the problem. I dont have many thing on the logs. Thanks a lot