I had this issue with one of my clients and it was an intermittent issue.
The main reason for this error was unknown at that time.
So, to overcome this issue, I had to perform certain troubleshooting steps in the Client's environment.
Most of the time we check the Services and Logs for possible information.
But, what I have learned from my experience, there is a pretty quick method of troubleshooting this issue.
If we run the Configuration Wizard on the affected Polling Engine, it will fully refresh all the files for the whole Orion platform.
What really happens is that the Configuration Wizard positively helps you to troubleshoot configuration issues of the Orion Services, Orion Database, Orion Website.
Restarting the Orion servers is not an option.
After you run the Configuration Wizard review the Orion Services for 04, 05 minutes.
Afterwards, you will be able to see the Additional Polling Engine is operational along with the Orion Web Console.
I just thought of sharing this experience which might be helpful for the community.
