OS is Trisquel 8.0 (Ubuntu 16.04 LTS derived), kernel 4.4.0-131-generic

I've reached the hair-tearing stage with ufw, which refuses to start up properly on system start.
Have tried:

* Editing /etc/ufw/ufw.conf to force enabled state.
* Editing /usr/share/ufw/ufw.conf to force enabled state.
* Editing /etc/rc.local
to add 'systemctl enable ufw'.
* Removing and reinstalling the ufw
package.

After a restart, the service reports 'active' but is actually inactive.

```
# service ufw status
[green bullet] ufw.service - Uncomplicated firewall
   Loaded: loaded (/lib/systemd/system/ufw.service; enabled; vendor preset: enabled)
   Active: active (exited) since Wed 2018-08-15 12:33:36 NZST; 15min ago
 Main PID: 389 (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/ufw.service
Aug 15 12:33:36 alcatraz systemd[1]: Started Uncomplicated firewall.

# ufw status
Status: inactive
# ping google.co.nz
ping: unknown host google.co.nz

# service ufw start
# service ufw status
[green bullet] ufw.service - Uncomplicated firewall
   Loaded: loaded (/lib/systemd/system/ufw.service; enabled; vendor preset: enabled)
   Active: active (exited) since Wed 2018-08-15 12:33:36 NZST; 15min ago
 Main PID: 389 (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/ufw.service
Aug 15 12:33:36 alcatraz systemd[1]: Started Uncomplicated firewall.

# service ufw start
# ufw status
Status: inactive

# service ufw restart
# ufw status
Status: inactive

# ufw enable
Firewall is active and enabled on system startup
# ufw status
Status: active
To                         Action      From
--                         ------      ----
192.168.1.0/24 21 on enp2s0 ALLOW       192.168.1.0/24
...
192.168.1.0/24 21          ALLOW OUT   192.168.1.0/24 on enp2s0
...
# ping google.co.nz
PING google.co.nz (216.58.196.131) 56(84) bytes of data.
64 bytes from syd15s04-in-f3.1e100.net (216.58.196.131): icmp_seq=1 ttl=52 time=64.2 ms

```

I'm no doubt missing something simple, but extensive googling has not revealed anything that helped. Please help with suggestions as to how to diagnose what's going wrong, or even better, a fix! :)