Today Solarwinds alerted us that 11 VMs (each one of them belonging on separate ESXi 6.0 'free' hosts). All the alerts were within 30 minutes or so of each other.
None of the VMs had actually rebooted. We are monitoring these VM in NPM as Windows nodes, as well as monitor their respective ESXi hosts.
The ESXi host monitoring is very recent (I added them to NPM just a few days ago) so I wonder if that could be a factor. There's no SNMP service running on the VMs. They all run Windows server 2008 Ent.