Modify /etc/udev/rules.d/40-permissions.rules back to its old state, without your workaround (/dev/lp0 should have owner root, group lp, and 660 permissions).
Now do
sudo aa-complain cupsd
Can you print now?
Can you post the messages containing "audit" in your /var/log/syslog?
You get back to the standard AppArmor configuration with
Can you try the following:
Modify /etc/udev/ rules.d/ 40-permissions. rules back to its old state, without your workaround (/dev/lp0 should have owner root, group lp, and 660 permissions).
Now do
sudo aa-complain cupsd
Can you print now?
Can you post the messages containing "audit" in your /var/log/syslog?
You get back to the standard AppArmor configuration with
sudo aa-enforce cupsd