Thanks for that command.... I will read futher on it.
During the maintenance period, we started to shutdown the guests, and most of them froze before being powered off. We did an hard reset on the host and it came back allright right after.
In the logs files in the scratch drive... there is no event recorded after the failure started.
HA managed to reboot some of our VMs... some we had to start manually, and 4 got their VMX file empty.... I had to reconstruct them from the logfile. After removing all the orphaned VMs, everything went back to the normal.