Tthere is an incompatibility between the RFC 4533 implementation of apacheDS and openldap.
openldap uses the cookie structure "rid=<replicaId>" (initial) or "rid=<replicaId>,csn=<Csn value>" (update) while apacheDS is using NULL for the initial state and the structure "<replicaId>;<Csn value>" for the update state. in the RFC its said:
The absence of a cookie or an initialized synchronization state in a cookie indicates a request for initial content.....
first is apacheDS like, second is openldap like
It should be possible to adapt the structure or the behavior.