Comment 2 for bug 1921750

Fix /etc/default/isc-dhcp-server helps:

Mar 29 17:13:41 mn-wifidhcp02 systemd[1]: Started ISC DHCP IPv4 server.
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Internet Systems Consortium DHCP Server 4.3.5
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Copyright 2004-2016 Internet Systems Consortium.
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: All rights reserved.
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: For info, please visit https://www.isc.org/software/dhcp/
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Config file: /etc/dhcp/dhcpd.conf
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Database file: /var/lib/dhcp/dhcpd.leases
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: PID file: /run/dhcp-server/dhcpd.pid
Mar 29 17:13:41 mn-wifidhcp02 systemd[1]: Reloading.
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Wrote 10210 leases to leases file.
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Listening on LPF/enp0s8.257/08:00:27:4d:fb:20/Guest
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Sending on LPF/enp0s8.257/08:00:27:4d:fb:20/Guest
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Listening on LPF/enp0s8.256/08:00:27:4d:fb:20/Employee
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Sending on LPF/enp0s8.256/08:00:27:4d:fb:20/Employee
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Listening on LPF/enp0s8.255/08:00:27:4d:fb:20/Guest-YYY
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Sending on LPF/enp0s8.255/08:00:27:4d:fb:20/Guest-YYY
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Listening on LPF/enp0s8.252/08:00:27:4d:fb:20/Guest-XXX
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Sending on LPF/enp0s8.252/08:00:27:4d:fb:20/Guest-XXX
Mar 29 17:13:41 mn-wifidhcp02 sh[13678]: Sending on Socket/fallback/fallback-net