We have Performance Center version 220.127.116.11. A few days ago PC stopped showing data for virtual machines for VMware Virtual Machine Aggregate Metrics.
How can I troubleshoot and find the root cause of the issue? I've tried to rediscover machine where VC AIM agent is, but nothing happened.
You may want to simply try restarting the data collectors to see if they start polling again. I would also add that 2.3.1 is end of service as of 2015: CA Performance Management releases 2.3.2 End of Service Announcement - CA Technologies
The current version is 3.0. There have been many changes since 2.3.1 that I think you would fine helpful. My suggestion would be to upgrade from 2.3.1 to take advantage of the many new features and bug fixes