Hey Ray, I just wanted to update you on the issue. I opened a ticket with VMware support, and right away he thought it was due to a stale host object in the database due to a host being removed from vCenter prior to uninstalling NSX. We checked out the vCenter database, as well as the MOB browser and confirmed that the host did not exist. Also, interesting to note that NSX Manager also has its own database separate from vCenter. You have to drop into root mode on the manager via the CLI with a special password that the support engineer had. He was fairly sure that there we would find the object here.. but we didn't.
After reviewing the log files, it turns out that his original hypothesis was true in that the errors were due to a host being removed prior to uninstalling NSX. He said that this is a bug in 6.2.0, which has been addressed in 6.2.1. The release notes shows:
NSX logging heartbeat failures for hosts that are not part of the NSX installation
When an NSX-prepared host is directly removed from the vCenter inventory (without first unpreparing it in NSX), NSX receives an unexpected 'Host Connected' DCN which causes partial removal of messaging infrastructure components from the host. As a result, the messaging link between NSX and the host may remain active when it should have been removed, and NSX may raise false 'Alert' SystemEvents for the host. This has been fixed in NSX 6.2.1.
He said the errors are purely cosmetic, so no need to immediately upgrade. I like things to be nice and neat though, so I'll be looking into getting the upgrade completed soon.