How to enable coredumps for BIND?

[ixbug at riseup.net]

Hello,

since named crashes I'd like to enable core dumps
for further analysis.

I added this to my options section of named.conf:

coresize unlimited;

and restarted named.

kern.corefile sysctl setting is:
/tmp/%N.core

but when I issue the following command to 
test if a core file gets created:
# kill -6 <PID of named>

no file is created in /tmp.

"ulimit -c" output is:
unlimited

Creating a core file using "gcore <pid>" works.

I assume dumpon is not relevant for non-kernel dumps:
$ dumpon -l
/dev/null

used version: bind913-9.13.5_2 (no chroot)
FreeBSD 12

Any help is appreciated.