[Samba] replication not done with missing DC?

[Jo L]

Hello,
I am running a total of three DCs with Samba, all running Version 4.3.11-Ubuntu (two actually the derivate Armbian). Now one of them crashed. Maybe I can recover the system, maybe I have to restore from a backup, but I know I cannot just run an older backup but instead should rejoin.
Now before continuing I was checking the consistency of the other two and figured out, they are not in sync. Some user data I created the last days is missing.
When I look into log.samba I can find both of the remaining DCs trying to connect to the missing one, but obviously they don´t try to connect directly.
How can I get them to talk to each other?
Thanks & Best Regards
Joachim