I updated some Nethservers (internet gateway, mail & appserver and a VPS) and it seems everything is working so far! 
Internet gateway (openvpn, ntop, squid, suricata):
There were some warnings:
Nov 30 15:05:59 server postfix: /usr/sbin/postconf: warning: /etc/postfix/master.cf: undefined parameter: submission_recipient_policy
Nov 30 15:05:59 server postfix: /usr/sbin/postconf: warning: /etc/postfix/master.cf: undefined parameter: submission_client_policy
Nov 30 15:50:24 server kernel: xt_ndpi: module verification failed: signature and/or required key missing - tainting kernel
Nov 30 15:51:16 server admin-todos: [ERROR] admin-todos: /etc/nethserver/todos.d/20ad_credentials exit code 31744
Mail & Appserver & AD (dokuwiki, guacamole, mattermost, nextcloud, omd, phpldapadmin, phpmyadmin, roundcube, rspamd, sogo, samba, webtop):
Warnings:
Nov 30 13:29:28 server2 dovecot: doveconf: Warning: /etc/dovecot/dovecot.conf line 272: Global setting mail_plugins won't change the setting inside an earlier filter at /etc/dovecot/dovecot.conf line 192 (if this is intentional, avoid this warning by moving the global setting before /etc/dovecot/dovecot.conf line 192)
Nov 30 13:29:28 server2 dovecot: doveconf: Warning: service auth { client_limit=2000 } is lower than required under max. load (2400)
Nov 30 13:29:28 server2 dovecot: Warning: service auth { client_limit=2000 } is lower than required under max. load (2400)
Nov 30 14:31:59 server2 clamd: LibClamAV Warning: Detected duplicate databases /var/lib/clamav/bytecode.cvd and /var/lib/clamav/bytecode.cld, please manually remove one of them
Internet gateway is joined to server AD, clients can access samba shares, permissions are working!
VPS with nextcloud and rspamd is working.
Additionally I updated another Nethserver (my backup storage) and a test VM (with nethserver-janus) and there were no errors.