@girish Thanks I wasn't aware of netplan.
A quick read of your links and editing the yaml file has sorted the problem for me.
As for the other comment I'm aware its a ubuntu problem, but as I only use Ubuntu for my cloudron server, I wasn't aware of netplan, or if changes to ethernet adapters would damage the configuration of all those veth for the cloudron apps. So I wanted to proceed cautiously in case something I was doing would break cloudron.
It would be pretty weird to require a platform, and refuse any assistance on the platform when issues arise. Especially so when (as per your link about systemd networking) there is so much useless information regarding generic linux help.