Ubuntu 20.04 eth Adapter Down Upon Boot, works with Lease Refresh

This is a bit of a strange one. Had a power outage, and after everything came back up (no physical damage), this Ubuntu box is starting up with the default/only eth adapter down. Upon a force dhclient lease refresh, it comes back up just fine.

Pertinent output below. Anyone run into this?:

Initial State:

    ifconfig -a
enp4s0: flags=4098<BROADCAST,MULTICAST>  mtu 1500
        ether ff:ff:ff:ff:ff:ff  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Running a dhclient -v to get that lease:

 sudo dhclient -v enp4s0
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/enp4s0/ff:ff:ff:ff:ff:ff
Sending on   LPF/enp4s0/ff:ff:ff:ff:ff:ff
Sending on   Socket/fallback
DHCPREQUEST for 192.168.0.6 on enp4s0 to 255.255.255.255 port 67 (xid=0x45190571)
DHCPREQUEST for 192.168.0.6 on enp4s0 to 255.255.255.255 port 67 (xid=0x45190571)
DHCPREQUEST for 192.168.0.6 on enp4s0 to 255.255.255.255 port 67 (xid=0x45190571)
DHCPACK of 192.168.0.6 from 192.168.0.1 (xid=0x71051945)
bound to 192.168.0.6 -- renewal in 39989 seconds.

After that... everything is up and running:

ifconfig -a
enp4s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.6  netmask 255.255.255.0  broadcast 192.168.0.255
        ether ff:ff:ff:ff:ff:ff  txqueuelen 1000  (Ethernet)
        RX packets 206  bytes 202417 (202.4 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 116  bytes 10053 (10.0 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Looking for a permanent solution.

This box doesn't have netplan installed, if that helps. I know most do.

I am not sure exactly what changed that broke the adapter's config, but after installing netplan.io, the adapter comes up with a lease from the dhcp server upon boot, as expected.

I understand that netplan is the currently accepted net management tool on Ubuntu. What I don't understand is what was managing that beforehand, and what changed to break it.