I have a multi-master openldap setup with 2 machines replicating a directory containing about 3.5 million entries.

I'm running openldap 2.4.31 on centos 6, and the directory is using the BDB backend.

Although the 2 machines are configured for multi-master syncrepl replication, in practice data is only written to one of the machines (I'll call it the master), 

and the second machine (which I'll call the slave) only gets data written by openldap replication.

Currently the contextCSN of the directory is the same from both machines, which (as I understand it) should mean that the directories are in sync, but I have written a program 

to compare what is in both directories which finds that there are 16 entries in the master directory not in the slave directory. I have double checked this

using ldapsearch on both directories.

I can't see any error messages in the openldap log and there doesn't appear to be any pattern connecting the entries which are missing from the slave. Most of the missing entries were

in the master directory before I created the slave machine and configured replication and have not changed.

The syncrepl config looks like this:

Are there any known issues with openldap replication which could result in missing data?

How can I force these missing entries to appear in the slave without rebuilding the whole of the slave directory and without changing the data in the master directory?

Chris