Wireguard interface gets no ipv4 address

[cpunk]

Wireguard has been working fine on this Kubuntu 20.04 install for a while. Now for some reason when I try to bring up a new interface with wg-quick, it gets no IP address assigned. Is anyone else seeing this when trying to create a new Wireguard interface?

Here's the ifconfig after it's brought up:

wg1: flags=209<UP,POINTOPOINT,RUNNING,NOARP>  mtu 1420
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 1000  (UNSPEC)
        RX packets 3  bytes 156 (156.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 25  bytes 22144 (22.1 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

There should be an IPv4 address, but there's none.

wg show output:

interface: wg0
  public key: <redacted> 
  private key: (hidden)
  listening port: 44429
  fwmark: 0xca6c

peer: <redacted>
  endpoint: 192.168.11.88:51820
  allowed ips: 0.0.0.0/0, ::/0
  latest handshake: 26 seconds ago
  transfer: 156 B received, 21.62 KiB sent

Here's the config file:

[Interface]
Address = 10.0.0.2/32
PrivateKey = <redacted> 
DNS = 8.8.8.8

[Peer]
PublicKey = <redacted> 
AllowedIPs = 0.0.0.0/0,::0/0
Endpoint = 192.168.11.88:51820

Right now I'm doing this just to test performance on a router that's acting as wg server. So I have it on a private network. There is some L2 traffic moving since I can see the handshake on the wg server and a few bytes moving.

I had another interface on this PC that was set up earlier, associated with a different endpoint, and it was still functioning fine. I could bring it up with "wg-quick up wg0" and it has the IP assigned and connectivity is working.

Thinking it was just a problem with interface creation I've tried the following:

1. Create the interface through the connections GUI in system settings. Same behavior. The IP is visible in the output of "nmcli -s c show wg1" and in /etc/NetworkManager/system-connections/wg1.nmconnection. Interestingly, the interface gets a link-local ipv6 address in this config, since ipv6 address mode is required (and disabled is not available in the GUI). Setting it to ignore gives a link-local that does respond to a ping. Still no ipv4.
2. Create the interface through nmcli. Same as above, the IP is in the stored configuration.
3. Next I removed all the Wireguard interfaces (including the working one), restarted, and then tried to set up only the previously-working interface wg0, with the same config file that was used previously (a 3 or so of months ago). That interface now has the same problem.
4. Thinking it could be caused by an update, I reverted the wireguard and wireguard-tools to the 20.04 release versions (apt-get install wireguard=1.0.20200319-1ubuntu1 wireguard-tools=1.0.20200319-1ubuntu1). Then I tried to wg-quick up that previously-working wg0.conf file. Same behavior. I upgraded back to current.

Any ideas about what might be happening? Can anyone else reproduce this?
Thanks for any ideas!

[cpunk]

FWIW I dropped back to release 20.04, then applied updates in batches, restarting and testing along the way. The problem has not recurred.