FreeBSD-12-ALPHA6: Network not starting at boot & can't start Plasma 5

I was running a fresh installation of 11.2-stable for the past couple of
weeks, and I decided to update from source to 12-current over the weekend.
After upgrading and rebooting, my network was no longer starting at boot.
It wouldn't work until I ran "service netif restart".

Also, after updating I made sure to run "pkg update && pkg upgrade" to
reinstall all my packages with ones compiled for FreeBSD 12. I restarted
again and tried to log into Plasma 5 from sddm. The screen went black for a
moment and immediately returned to the sddm login screen. I removed and
reinstalled all packages on my system to see if maybe there was a stale
config file left over or something. The login problem persisted. It worked
fine under 11.2-stable

Thinking perhaps I might have made a mistake in upgrading from source, I
downloaded the 12-ALPHA6 snapshot, loaded it onto a USB stick, and did a
fresh installaton. The problem with network not starting at boot persists.
I haven't done a full install of Plasma 5 yet to test it again.