Named chroot with Apparmor
Apparmor. Random silent failures? It's apparmor's fault.
Add the following to /etc/apparmor.d/local/usr.sbin.named
# BIND9 chroot in /var/named/wan_chroot /var/named/wan_chroot/** r, /var/named/wan_chroot/dev/null rw, /var/named/wan_chroot/var/** rw,
And reload config. Confirm it worked.
$ sudo service apparmor reload