check if you are sending any traps or syslog to that poller from your monitored devices. check also your polling time on the said poller.
When you say through Netflow, do you have NTA installed?
If so, where is it installed?
What did you upgrade from/to?
What other modules do you have installed/in use?
How is your Orion environment setup?
Primary Server: NPM, NCM, SAM
Secondary Server: APE, NTA
DB Server: Database
we're using the netflow from manage enginee, not the one found in orion. we have recently upgrade the orion npm to 11.0.1, ncm, sam and ipam, we did a 2 level upgrade. we have a primary server (web as well), a db server and 2 other secondary poller