AFAIK, those messages are harmless and appear when the smwingsd service is stopped.
Check if it’s running and restart if it is not.
# systemctl status smwingsd
● smwingsd.service - Server Manager DB cache Daemon
Loaded: loaded (/usr/lib/systemd/system/smwingsd.service; static; vendor preset: disabled)
Active: active (running) since Tue 2018-05-15 11:43:35 CEST; 1 day 1h ago
Docs: https://github.com/NethServer/nethserver-httpd-admin
Main PID: 1062 (smwingsd)
CGroup: /system.slice/smwingsd.service
└─1062 /usr/bin/perl /usr/libexec/nethserver/smwingsd
systemctl restart smwingsd