Hello,
I was able to perform "Warm" migrate from either the slave or the master.
Yes the master was rebooted.
@henri9813 Did you reboot the master after it was updated? If yes, I think you should be able to migrate back the VM's to the master, and then continue patcting the rest of the hosts.
No, i would migrate back vm from MASTER (updated ) to slave ( not updated ), but wasn't working.
Only warm migrations works.