VMware's CBT Bug for ESXi
VMware confirmed there's a bug that can cause an outage in your VMs if you're using ESXi 6.0 and Hardware Version 11 on your VMs. This only occurs if you're using Change Block Tracking to backup your VMs. So, while you could avoid this problem by just turning off CBT or by doing a full backup it could be a nuisance.
On Nov. 26th VMware did anounce a patch to fix this bug, but it does require that you restart your VMs. VMware customers are infamous for upgrading their vSphere environments almost immediately after a new release becomes availaable, but it seems vSphere 6.0 has been a bit buggy. These bugs don't seem to be life-ending or anything like that...but no one likes to reboot their VMs in the middle of the day.