How to set a static IP using netplan? (running freshly installed Ubuntu Bionic server)

[mrjayviper]

I've followed/looked at several guides (like this one) and the netplan example page on how to do the above.

My problem is that no static IP is getting assigned to the built-in ethernet port. I have run

netplan apply

several times. I've also rebooted the PC and still no luck.

I am sure the ethernet port works as I was previously using it on Ubuntu 16.04 just before I decided to fresh install 18.04.2.

Any ideas what I could be doing wrong? I am going to use the ethernet port to connect my main PC to the Ubuntu server via a crossover cable.

If I set the ethernet port to use

dchp4:true

and connect an ethernet cable from it to my modem/router and disable my WiFi card (by removing the netplan config), the PC can connect to the net without any issues.

Thanks

Edit: I had a look at /run/systemd/network/config-file-here and it looks correct to me. At the very least representative of the contents of the YAML file. /run/systemd/network folder was mentioned in the netplan website troubleshooting page.
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This is the output of

netplan --debug apply

which also shows the contents of my YAML files. I have tried with and without dhcp4/dchp6/gateway4/renderer.