I faced a unique situation where-in some of the ESXi hosts when rebooted via different methods (vCenter, ESXi web interface, ssh, iLO (DCUI)) did not reboot and had to be reset via the iLO. Post
reset the host came up fine but did not auto connect to vCenter, I had to manually connect and supply the ESXi root credentials again.
Now when I again rebooted the host (via vCenter),this time the host rebooted fine as viewed via the iLO console, and also auto connected fine to the vCenter.
So in what scenario host will not reboot and when cold rebooted (reset) why will it not connect to the vCenter ? Note that the ESXi root credentials have not changed.