Comment 3 for bug 1833400

Odd, I've seen really (I mean really) old reports with the same signature [1]
The attribute [2] seems to be DNS_DISPATCHATTR_NOLISTEN - anything in that regard in your configs?

Code seems to be this:
3685 void
3686 dns_dispatch_importrecv(dns_dispatch_t *disp, isc_event_t *event) {
3687 »···void *buf;
3688 »···isc_socketevent_t *sevent, *newsevent;
3689
3690 »···REQUIRE(VALID_DISPATCH(disp));
3691 »···REQUIRE((disp->attributes & DNS_DISPATCHATTR_NOLISTEN) != 0);
3692 »···REQUIRE(event != NULL);

18.04 is quite different and less fatal for the same condition
3718 void
3719 dns_dispatch_importrecv(dns_dispatch_t *disp, isc_event_t *event) {
3720 »···void *buf;
3721 »···isc_socketevent_t *sevent, *newsevent;
3722
3723 »···REQUIRE(VALID_DISPATCH(disp));
3724 »···REQUIRE(event != NULL);
3725
3726 »···if ((disp->attributes & DNS_DISPATCHATTR_NOLISTEN) == 0)
3727 »···»···return;

Thanks to git I was able to find changes [3][4] which seem to fix this issue.
This lead to the issue [5] which I can't read for permissions in their bug system :-/

Since the expected Fix is in Bionic (sine 9.10.6 [6] to be specific) I'll mark only Xenial as affected for now.

I had hoped that the bug might have instructions to recreate the issue.

@Douglas / Heikki - do you have any means to trigger this bug so that we could verify with a potential fix backport with a PPA ?

@Douglas / Heikki - it mentions that this is a race on shutdown, was your server restarted around that time?

[1]: https://sourceforge.net/p/bind-dlz/mailman/message/6537634/
[2]: http://users.isc.org/~each/doxygen/bind9/dispatch_8h.html#73469a6ec10db29033bb0da2d8acb31c
[3]: https://gitlab.isc.org/isc-projects/bind9/commit/019132b70c368bc9abca0034d07b324bb7cb6eb2
[4]: https://gitlab.isc.org/isc-projects/bind9/commit/a94d68ce432b9e11c4ae91d48ee257b1675f86d7
[5]: https://bugs.isc.org/Public/Bug/Display.html?id=43822
[6]: https://abi-laboratory.pro/?view=changelog&l=bind&v=9.10.6