Apparently the issue is caused by this commit https://gitlab.isc.org/wpk/bind9/commit/65a483106e45704e19781bfe4f4634db4f77562e which fixes a bug in the ISC heap library.
There seems to be a double-deletion of the released addresses in the dhcpv6 code.
This quick-and-dirty patch helps (on ubuntu 18.04.1).
Apparently the issue is caused by this commit https:/ /gitlab. isc.org/ wpk/bind9/ commit/ 65a483106e45704 e19781bfe4f4634 db4f77562e which fixes a bug in the ISC heap library.
There seems to be a double-deletion of the released addresses in the dhcpv6 code.
This quick-and-dirty patch helps (on ubuntu 18.04.1).