There are some ongoing issues with yesterday’s upstream release: CentOS 7.6.1810
Check your samba version:
[root@host ~]# rpm -q samba
samba-4.8.3-4.el7.x86_64
If that matches you have two options
a) downgrade with yum history undo last
b) upgrade to NethServer 7.6.1810 beta (some packages for firewalls are still on QA)
yum install http://packages.nethserver.org/nethserver/7.6.1810/updates/x86_64/Packages/nethserver-release-7-9.ns7.noarch.rpm
echo '7.6.1810' > /etc/yum/vars/nsrelease
yum clean all
yum update
See also this Bug