Comment # 1 on bug 1205303 from Christian Boltz

Can you please switch winbindd to complain mode with
    aa-complain /etc/apparmor.d/usr.sbin.winbindd
and then try again? This should give you quite some log entries in audit.log.

Then either attach your audit.log to this bugreport, or use aa-logprof to
create a profile for samba-gpupdate yourself, and attach the profile ;-)
(Note: first step will be to allow executing samba-gpupdate in the winbindd
profile. Please use Px (= "(P)rofile" in aa-logprof) for that.)