Comment 1 for bug 1988657

I just tried it on all releases up to Kinetic, they're all affected. I suspect it's actually a bug in systemd-networkd, as the files generated in /run/systemd/networkd/ look sane enough:

root@firm-mayfly:~# cat /run/systemd/network/10-netplan-eno1.network
[Match]
MACAddress=00:16:3e:10:7a:c2
Type=!vlan bond bridge

[Network]
LinkLocalAddressing=ipv6
Address=192.168.2.1/24
VLAN=l2club

root@firm-mayfly:~# cat /run/systemd/network/10-netplan-l2club.netdev
[NetDev]
Name=l2club
Kind=vlan

[VLAN]
Id=10

root@firm-mayfly:~# cat /run/systemd/network/10-netplan-l2club.network
[Match]
Name=l2club

[Network]
LinkLocalAddressing=ipv6
Address=10.232.228.16/8
ConfigureWithoutCarrier=yes

There wasn't anything suspicious in the journald logs, either.