At some point I noticed that vMotion for several VMs failed with message “Failed to receive migration”.
After some investigation I discovered that VM advanced setting “mks.enable3d” had been changed from TRUE to FALSE without powering off the VM. After power cycling the VM vMotion started to work again. But I was not able to power cycle all the VMs so I changed the mks.enable3d setting value back to TRUE and then vMotion also started to work again.
I guess that’s why you should change advanced settings on powered off VMs instead of powered on VMs.