Hi everybody,
Got the same issue here with 5.1 Hosts.
It happened to many of my hosts in different clusters.(All in 5.1 by the way).
Support didn t investigate that much considering i had storage issues which should be solved first.
The known work around is to restart managment Agent in CLI:
/sbin/services.sh restart
But this is not a solution to this issue and its side effects are really annoying (HA and DRS focusing to gather Vms on remaining visible Hosts) which kills perforance because of unbalanced cluster.
Impacted ESX isn taken in consideration at all by vcenter.
I think i m going to open an other case with vmware support wishing they have a real answer this time.
Thanks to those who can provide some help.
Jean-Michel