Last night during a patching job in a customer I found the following error for several VMs when I put a host in maintenance mode and DRS tried to evacuate the virtual machines to the other nodes of the cluster.
Very strange since as far as I could see the virtual machines were running without errors, I was logged into some of them through SSH, and they also appeared as powered on in vSphere Client.
I decided to go to Tech Support Mode on the ESXi and check the virtual machine power state.
Everything looked exactly as it should be, no error logs, nothing. At this point I decided to restart the ESXi management agents.
And it worked, after a few seconds I was able to perform a successful vMotion and the host could be evacuated.