slapd[21334]: do_syncrepl: rid=010 rc -2 retrying (4 retries left) olcSyncrepl: {0}rid=010 provider=ldap://ldap binddn="cn=config" bindmethod=simple credentials=XXX searchbase="cn=config" type=refreshAndPersist retry="5 5 300 5" timeout=1 slapd-2.4.23 on master & slave

This happens when the slave server is restarted. If make some change to cn=config, then the error disappear.

I didn't find any explanation about rc -2. What this is about?