Just looked at what netplan generates in networkd:
[Match] Name=eth0
[Network] DHCP=ipv4 IPv6AcceptRA=no
[DHCP] RouteMetric=100
So that shows it's explicitly disabling IPv6 RA handling on the interface, causing the regression.
Just looked at what netplan generates in networkd:
[Match]
Name=eth0
[Network]
DHCP=ipv4
IPv6AcceptRA=no
[DHCP]
RouteMetric=100
So that shows it's explicitly disabling IPv6 RA handling on the interface, causing the regression.