From forum: https://forum.vyos.io/t/dhcp-hostnames-of-clients-not-resolving-after-update-v1-2-3-1-2-rolling/4393
There seems to be a bug in v1.2.3: the first entry in the hosts file is missing a carriage return and then it fails to resolve that hostname. the subsequent ones will work though.
admin@vyos:~$ cat /etc/hosts ### Autogenerated by VyOS ### ### Do not edit, your changes will get overwritten ### # Local host 127.0.0.1 localhost 127.0.1.1 vyos.lan vyos # The following lines are desirable for IPv6 capable hosts ::1 localhost ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters # From DHCP and "system static host-mapping"192.168.1.150 macosmini.lan #on-dhcp-event 00:00:0F:11:11:11 192.168.1.150 macmini.lan #on-dhcp-event 00:00:0F:11:11:11