Aggregation doesn't start on a newly added concentrator because of wrong entries in NwBroker.cfg.
The below error message appears in /var/log/messages of concentrator:
Jan 18 07:01:34 SASRV NwBroker: [Aggregation] [failure] Failed to complete device '10.192.6.16:50005' because MergeInfo failed because local data from device '10.192.6.16:50005' was invalid. Device returned lsStart:1 lsEnd:3678 lmStart:1 lmEnd:29424 last:0. Device aggregation is being stopped. Jan 18 07:01:34 SASRV NwBroker: [Broker] [info] Device '10.192.6.16:50005' mapping file saved Jan 18 07:01:34 SASRV NwBroker: [Thread] [info] Stopped thread: Aggregation State Schedule 10.192.6.16:50005 id: 43300 Jan 18 07:02:04 SASRV python: update-federation-links.py: No changes needed
In /var/netwitness/ng/NwBroker.cfg, you will find two entries for the concentrator with different port numbers and aggregation doesn't start.