vnet/jail crashdump

Hi,

After stopping a jail I get a crashdump.
core.txt:  
https://www.klop.ws/core_2eef39c581f90f2f0c4921e43f1998c1/core.txt.0

Jail.conf:
----------
exec.stop = "/bin/sh /etc/rc.shutdown";
exec.clean;

exec.prestart = "ifconfig bridge0 > /dev/null 2> /dev/null || ( ifconfig  
bridge0 create && ifconfig bridge0 addm vtnet0 && ifconfig bridge0 up)";

exec.consolelog = "/var/log/jail_${name}_console.log";

mount.devfs;
path = "/data/jails/$name";
host.hostname = "$name";
mount.fstab = "/data/jails/fstab.$name";
vnet;
allow.mlock;
devfs_ruleset="110";

freebsd12 {
	osrelease = 12.1-RELEASE-p4;
	osreldate = 1201000;
	vnet.interface = "epair0b";
	# make sure the exec.prestart has a "+=" as we de it in the global  
definition
	# when checking for the bridge
	exec.prestart += "ifconfig epair0 create up";
	exec.prestart += "ifconfig bridge0 addm epair0a";
	exec.prestart += "ifconfig epair0b link 02:xxxxxx:0c";
	exec.start = "dhclient epair0b";
	exec.start += "/bin/sh /etc/rc";
	exec.poststop  = "ifconfig bridge0 deletem epair0a";
	exec.poststop += "ifconfig epair0a destroy";

}
freebsd13 {
	vnet.interface = "epair1b";
	# make sure the exec.prestart has a "+=" as we de it in the global  
definition
	# when checking for the bridge
	exec.prestart += "ifconfig epair1 create up";
	exec.prestart += "ifconfig bridge0 addm epair1a";
	exec.prestart += "ifconfig epair1b link 02:xxxxxx:0d";
	exec.start = "dhclient epair1b";
	exec.start += "/bin/sh /etc/rc";
	exec.poststop  = "ifconfig bridge0 deletem epair1a";
	exec.poststop += "ifconfig epair1a destroy";
}
----------

What can I do to help debug?

Regards,
Ronald.