You can follow the procedure below to set up debug and collect debug info:
1) 1) Set NH_DBG_OUTPATH to $NH_HOME/log/advanced
2) Turn on advanced logging for replication on the RFE (the report console)
3) Run $NH_HOME/bin/sys/nhiSynchronize -cluster –checkContext from RFE to reproduce the duplicate error
4) Then run nhGetSupportInfo -type replication, and post the zip file created into the ticket
Also please get a history of what changes to the cluster machines had been made recently.