@olivierlambert Dang ok. I waited a few minute then clicked the Connect in XOA for that host and it connected. Not sure what to do really.

So you have to dig in the SMlog to check what's going on

About the xsconsole: sometimes it's not refreshing. You can try to get access to the console, then type "xsconsole" it will start it and you should see it works You must have the master up to date if you want your slave to connect again. I never tried to elect a new master in the middle of the upgrade, I would discourage it. Better shutdown some VMs on the master, upgrade it and you are automatically back on track.

Then try to find anything happening around that time on other hosts, equipment, storage and so on.