I've 2 hosts running hosted engine VM only. One of the 2 hosts is also providing storage over NFS. At boot this morning, the host providing storage is in failed state due to bug #1670312. In engine (running on the other host) I see the failing one with upgrade available despite yum update is not showing any update. In order to fix it I tried to move the host to maintenance and I got the following message: Operation Canceled Error while executing action: Cannot switch Host to Maintenance mode. Host still has running VMs on it and is in Non Responsive state. It's true that it's in non responsive state, but it's false it has running VMs on it.
*** This bug has been marked as a duplicate of bug 1574443 ***