Comment 3 for bug 1724895

So the only thing I see in the logs that looks suspicious is:

Jan 30 13:30:49 bridgevm systemd-udevd[376]: Config file /run/systemd/network/10-netplan-br0devs.link matches device based on renamed interface name 'ens8', ignoring

(my setup is explained in https://bugs.launchpad.net/ubuntu/+source/nplan/+bug/1746246)

The MTU setting is in that file, so if it is ignored it would stand to reason that the MTU would fail to apply.

It looks like this would apply to *all* renamed interfaces, which I think is lots these days.