[Samba] after a couple of year of success is not possible to add workstations to domain

[Massimo Donato - Adcom.it]

*/Hi all,
    after a couple of year of successfully working samba AD DC is  not 
possible to add workstations to domain
since a few day ago in windows i get a messagge complaining that the 
account previously exists. ant that to try access with a different account.
after some investigation i found that the backupDC  was in hardware fault.
the primary seems to work great, but still unable to add workstation to 
domain.
seems like something is missing,
samba version is 4.7.4(upgraded during investigation)

any advice ? where to look ?



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