The following alerts about handle counts are raised:
"Health Service (Monitoring Host) Handle Count has exceeded the threshold" or "Health Service Handle Count has exceeded the threshold" on collector server.
The monitors raising the mentioned alerts ensure that the "Process\Handle Count" counter for the "MonitoringHost.exe" and "HealthService.exe" processes does not exceed a specific threshold over a series of consecutive samples. If the conditions are met, this monitor will change to a critical state, which will then roll up to the "Health Service State" monitor.
In the Veeam MP case, the values that trigger the monitor may result from Collector server overload. If too many VMware hosts and VMs are monitored, then the Health Service may be overwhelmed when processing the data.
Current amount of handle counts can be checked using Windows Task Manager on the collector server:
1) Start Windows Task Manager and switch to the Processes tab
2) Choose View -> Select columns and enable Handles
After that you should be able to see a column named "Handles"