MTU specified in netplan is not applied at boot

My netplan file looks like so:

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses:
        - 169.254.1.1/24
      mtu: 9000

After boot the eth0 interface takes the configured address, but the MTU is the default value of 1500.

If I run sudo netplan apply manually after boot, then the MTU increases to 9000 as expected.

Right after boot, the generated files for systemd-networkd look like so. These files do not change after manually applying the second time.

$ cat /run/systemd/network/10-netplan-eth0.link
[Match]
OriginalName=eth0

[Link]
WakeOnLan=off
MTUBytes=9000

$ cat /run/systemd/network/10-netplan-eth0.network
[Match]
Name=eth0

[Network]
Address=169.254.1.1/24

Nothing obvious stands out to me in the log of systemd-networkd, other than the order being different:

# at boot
Dec 13 06:29:35 ifcb110 systemd-networkd[3233]: eth0: IPv6 successfully enabled
Dec 13 06:29:35 ifcb110 systemd-networkd[3233]: eth0: Link UP
Dec 13 06:29:38 ifcb110 systemd-networkd[3233]: eth0: Gained carrier
Dec 13 06:29:39 ifcb110 systemd-networkd[3233]: eth0: Gained IPv6LL
Dec 13 06:29:39 ifcb110 systemd-networkd[3233]: eth0: Configured

# second time that works
Dec 13 06:39:46 ifcb110 systemd-networkd[6781]: eth0: Gained IPv6LL
Dec 13 06:39:46 ifcb110 systemd-networkd[6781]: eth0: Link is not managed by us
Dec 13 06:39:46 ifcb110 systemd-networkd[6781]: eth0: IPv6 successfully enabled
Dec 13 06:39:49 ifcb110 systemd-networkd[6781]: eth0: Gained carrier
Dec 13 06:39:49 ifcb110 systemd-networkd[6781]: eth0: Configured

Here's what netplan --debug apply outputs (abridged):

$ sudo netplan --debug apply
** (generate:7015): DEBUG: 06:50:14.054: Processing input file //etc/netplan/config.yaml..
** (generate:7015): DEBUG: 06:50:14.054: starting new processing pass
** (generate:7015): DEBUG: 06:50:14.054: eth0: setting default backend to 1
** (generate:7015): DEBUG: 06:50:14.054: Generating output files..
** (generate:7015): DEBUG: 06:50:14.055: NetworkManager: definition eth0 is not for us (backend 1)
DEBUG:netplan generated networkd configuration exists, restarting networkd
DEBUG:no netplan generated NM configuration exists
DEBUG:device eth0 operstate is up, not replugging
DEBUG:netplan triggering .link rules for eth0

What might be preventing the setting from taking effect the first time?

(I suspect something like a race between the eth0 interface becoming available and applying the udev rules in the .link file.)

It sounds a bit like this bug which was closed a few years ago, but the problem still occurs for me.

Instead I ended up making a fix-mtu@.service unit file containing

[Unit]
Description=Fix MTU on Interface

[Service]
Type=oneshot
ExecStart=/sbin/ip link set dev %i mtu 9000

[Install]
WantedBy=sys-subsystem-net-devices-%i.device

I'm not really pleased with this workaround because it seems like systemd-networkd is supposed to do this for me.