multiples syncrepl from same host and DB

hello,

I wanted to synchronize 2 branches of a master DB (slapd-2.4.38). So I created 2 olcSyncrepl on the slave :

olcSyncrepl: {0}rid=201 provider=ldap://master searchbase="cn=branch1,suffixDB" scope=sub olcSyncrepl: {1}rid=202 provider=ldap://master searchbase="cn=branch2,suffixDB" scope=sub

Unfortunatly, it doesn't work. A change on branch2 on the master produces often a "CSN too old" on the slave.

After investigating, it seems that the pb comes from the fact there is one contextCSN by DB. So if the sync task on branch1 is the first to process, it updates the contextCSN and therefore the sync task on branch2 thinks that change is not newer. Am I right ?

So is there a proper way to achieve what I want ?

Thank for any hints,