Network Oddities since upgrading from 18.04 -> 20.04 (Persistent DHCP)

Question

Apologies if this has been beaten to death. I've done about 6 hours of searching and testing myself and pulling my hair out.

After a backup, I reluctantly agreed to upgrade from 18.04 to 20.04. Aside from having to fix a few custom packages, things were generally OK.

First issue was a lack of DNS. I honestly can't remember now how I fixed it. However, I think it's related to my main issue.

I run this host in a static IP configuration. However, upon upgrade, I see a secondary address via DHCP on the ethernet interface (enp0s3). No matter what I do, I can't seem to shake it.

Even more odd: Within Gnome (which I've always avoided before), if I delete that connection (called enp0s3), it just comes back on its own. "Wired Connection 1" is my static interface.

Another possible clue, even if I slide the slider to disable the network connection, it just slides back over to enabled/green on its own within a few seconds.

I'm wondering if I'm getting conflicts between NetworkManager, Netplan, or Networkd

Thanks for any insight.

sudo lshw -C network

  *-network
       description: Ethernet interface
       product: 82540EM Gigabit Ethernet Controller
       vendor: Intel Corporation
       physical id: 3
       bus info: pci@0000:00:03.0
       logical name: enp0s3
       version: 02
       serial: 08:00:27:ab:a2:8f
       size: 1Gbit/s
       capacity: 1Gbit/s
       width: 32 bits
       clock: 66MHz
       capabilities: pm pcix bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=e1000 driverversion=7.3.21-k8-NAPI duplex=full ip=192.168.34.25 latency=64 link=yes mingnt=255 multicast=yes port=twisted pair speed=1Gbit/s
       resources: irq:9 memory:f0000000-f001ffff ioport:d010(size=8)

cat /etc/network/interfaces

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

cat /etc/netplan/*.yaml

# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager

ip a

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 08:00:27:ab:a2:8f brd ff:ff:ff:ff:ff:ff
    inet 192.168.34.25/24 brd 192.168.34.255 scope global noprefixroute enp0s3
       valid_lft forever preferred_lft forever
    inet 192.168.34.12/24 brd 192.168.34.255 scope global secondary noprefixroute enp0s3
       valid_lft forever preferred_lft forever
    inet6 fe80::80e1:7fc:b61a:cd41/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

root@homeauto03:/etc/NetworkManager/system-connections# ls -altr

total 12
drwxr-xr-x 7 root root 4096 Nov 30 21:09  ..
-rw------- 1 root root  393 Dec  1 13:47 'Wired connection 1.nmconnection'
drwxr-xr-x 2 root root 4096 Dec  1 16:24  .

root@homeauto03:/etc/NetworkManager/system-connections# cat Wired\ connection\ 1.nmconnection

[connection]
id=Wired connection 1
uuid=358648bf-1c3e-3704-995a-300a184d0445
type=ethernet
autoconnect-priority=-999
interface-name=enp0s3
permissions=
timestamp=1606848238
[ethernet]
mac-address-blacklist=
[ipv4]
address1=192.168.34.12/24,192.168.34.1
dns=8.8.8.8;8.8.4.4;
dns-search=
ignore-auto-dns=true
method=manual
[ipv6]
addr-gen-mode=stable-privacy
dns-search=
method=auto
[proxy]
root@homeauto03:/etc/NetworkManager/system-connections#

tbully@homeauto03:~$ ip a

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 08:00:27:ab:a2:8f brd ff:ff:ff:ff:ff:ff
    inet 192.168.34.12/24 brd 192.168.34.255 scope global noprefixroute enp0s3
       valid_lft forever preferred_lft forever
    inet 192.168.34.25/24 brd 192.168.34.255 scope global secondary noprefixroute enp0s3
       valid_lft forever preferred_lft forever
    inet6 fe80::80e1:7fc:b61a:cd41/64 scope link noprefixroute
       valid_lft forever preferred_lft forever
tbully@homeauto03:~$

Manager Settings ipv4

TEMPORARY SOLUTION

1. executed systemctl stop dhcpcd.service
2. removed connection profile in NetworkManager
3. noted that both pings stopped working - .12 (static) and .25 (dhcp) assigned
4. also noted that the enable button didn't go back to green on its own (and connection being re-enabled) did not occur as it did before
5. recreated the manual ipv4 connection (.12).
6. pings started back up for .12
7. noted that .25 (or any other dhcp address) did not reassign
8. excuted systemctl disable dhcpcd.service
9. survived reboot

Reveresed these steps (re-enabled the DHCP client) and the problem returned.

Nuke option but it'll work for now until I (or someone) can figure out a more proper solution.