vm-bhyve: abort trap before OpenBSD install

Hello,

I'm trying to fire up an OpenBSD VM with sysutils/vm-bhyve but 
unfortunately it fail.
I have a grub menu but if I press enter I get this result :

# vm install -f obsd-test install71.iso
Starting obsd-test
   * found guest in /zroot/bhyve/obsd-test
   * booting...
Abort trap

I run a FreeBSD 13.1, below is the template I used :

# cat openbsd71.conf
debug="on"
loader="grub"
cpu=1
memory=256M
network0_type="virtio-net"
network0_switch="public"
disk0_type="virtio-blk"
disk0_name="disk0.img"
grub_install0="kopenbsd -h com0 /bsd.rd"
grub_run0="kopenbsd -h com0 -r sd0a /bsd"
bhyve_options="-w"

The root directory of install71.iso :

# ls -l ./*
-r--r--r--  1 root  wheel      126 Apr 12 05:25 ./TRANS.TBL
-rw-r--r--  3 21    wheel  2810843 Apr 12 03:51 ./bsd
-rw-r--r--  3 21    wheel  2810843 Apr 12 03:51 ./bsd.rd

./7.1:
total 4
-r--r--r--  1 root  wheel    43 Apr 12 05:25 TRANS.TBL
drwxr-xr-x  2 root  21     4096 Apr 12 05:25 alpha

/var/log/messages :

Aug 14 21:29:47 bhyve-01 kernel: tap0: Ethernet address: 
58:9c:fc:10:ff:c7
Aug 14 21:29:47 bhyve-01 kernel: tap0: promiscuous mode enabled
Aug 14 21:29:49 bhyve-01 kernel: tap0: link state changed to UP
Aug 14 21:29:49 bhyve-01 kernel: vm-public: link state changed to UP
Aug 14 21:29:49 bhyve-01 kernel: pid 38521 (bhyve), jid 0, uid 0: exited 
on signal 6
Aug 14 21:29:49 bhyve-01 kernel: tap0: link state changed to DOWN
Aug 14 21:29:49 bhyve-01 kernel: vm-public: link state changed to DOWN

If I read correctly signal(3), the signal 6 means "SIGABRT: abort 
program (formerly SIGIOT)", but that doesn't help me much.

Snippet of /boot/loader.conf :

vmm_load="YES"
nmdm_load="YES"
if_tap_load="YES"
if_bridge_load="YES"
bridgestp_load="YES"

Can someone have any idea about what went wrong with my setup ? :)

Have a nice day,

-- 
Rollniak (Yan)