Hard to know what's going on without more information. Usually we would remove the whole machine all the way down to the chassis, meaning the iLOM. If a SR was opened, we could even do a live session and check the domain model to see if any leftovers were present. Then, everything should work upon re-discovery. It seems possible that you might have some leftovers here.
I would try removing the agent on the machine. Do a full and complete unconfigure and uninstall. Then, try a reinstall and reconfigure of the agent. If that doesn't work, then open a SR, and we'll figure it out.
How To Remove and Re-install Ops Center Agent Software on a Control Domain to Rebuild LDOM Guest Metadata (Doc ID 2355347.1)
To install an agent:
Please read the documentation provided. Many possible situations are addressed there. My notes would be far longer if I addressed each OS revision and customer configuration.