Comment 1 for bug 1939884

I know apparmor_parser mostly from the outside ("wrong" programming language for me) and I also don't know too much about Debian, therefore I'll un-assign myself.

Let me try with a wild guess nevertheless:

Do you see this error on boot or (also) on "systemctl reload apparmor"?
Do you have a separate partition for /var/ or /var/cache/?

If you see the error only on boot and have a separate partition, my guess is that this partition is mounted _after_ AppArmor gets started - and therefore /var/cache/apparmor/ is not available (yet).