Can I suggest you open a case with HP support so this can be investigated.
With SNMPv3 there is a protocol setup exchange of packets where NNMi has to learn the remote agents EngineID, EngineTime and Boot count. This exchange can take a different number of packets depending on how the agent has been implemented. Sadly with all standards we have seen them interpreted in different ways.
In order to address you situation we will need to get some network traces to see what is happening with this protocol establishment, especially when it is failing.
All the best
HP Support Viewed the Support tips? Search for "(NNMi) Support Tips" and order by Date to get the list The views expressed in my contributions are my own and do not necessarily reflect the views and strategy of HP If you find this or any post resolves your issue, please be sure to mark it as an accepted solution.