Thank you for using Ubuntu and taking the time to report a bug.
ufw saves its files as iptables-restore style files (/etc/ufw/before*rules, /lib/ufw/user*rules and /etc/ufw/after*rules). Can you run the following commands and attach the resulting file (/tmp/521358.txt):
$ sudo sh -x /lib/ufw/ufw-init stop > /tmp/521358.txt 2>&1
$ sudo sh -x /lib/ufw/ufw-init start >> /tmp/521358.txt 2>&1
Thank you for using Ubuntu and taking the time to report a bug.
ufw saves its files as iptables-restore style files (/etc/ufw/ before* rules, /lib/ufw/user*rules and /etc/ufw/ after*rules) . Can you run the following commands and attach the resulting file (/tmp/521358.txt):
$ sudo sh -x /lib/ufw/ufw-init stop > /tmp/521358.txt 2>&1
$ sudo sh -x /lib/ufw/ufw-init start >> /tmp/521358.txt 2>&1