I see that some entryCSN have not been synced properly with the provider. 

I run multimaster setup and with several slaves and sometimes i see that some slaves have old entryCSNs and I am syncing them manually with -c option. 

I haven't been able to track the cause nor see anything in the log to indicate the problem. However, we have had slapd become non-responsive due to IO blocking on logging. Could this cause syncrepl to miss updating the entries?  Has anyone seen this behaviour? 

Thanks