I have experienced it before and perform the ff test
1. Check if the polling engine is with the same version with the primary server
start > progam files > solarwind orion > advanced features > monitor polling engine
if not. download the new version on the customer portal and apply it to all polling engine
2. Check if all services on each polling engine is running. If one service is in stopped mode then you can see the polling engine in red on your monitor polling engine
start > program files > solarwinds orion > advanced features > Orion service manager).
i.e syslog services. do take note that in NPM 9.1 SP5 Alert manager by default is stopped in all polling engine except on your primary server or web server
3. Restart the polling engine
4. Review polling completion percentage ( http://www.solarwinds.com/support/orion/docs/gaps/gaps.htm )
- Log on to the Orion server.
- Click Start > All Programs > SolarWinds Orion > Database Utilities > Database Manager.
- Expand your Orion database in the left navigation tree, and then click Engines.
- Click Table > Query Table in the menu bar.
Select PollingCompletion from Enginesin the Query window, and then click Refresh.
5. Try to stopped and restart the solarwind network performance monitor and solarwind syslog services on Monitor Polling Engines. It will take some time before it goes to running state because of synchronization with the database
Hope it will help
Thanks this is very helpful