Hmm, backtrace is similar but not identical:
db:0:kdb.enter.default> bt
Tracing pid 96484 tid 100231 td 0xfffff8006f46e740
kdb_enter() at kdb_enter+0x37/frame 0xfffffe002eb0b630
vpanic() at vpanic+0x197/frame 0xfffffe002eb0b680
panic() at panic+0x43/frame 0xfffffe002eb0b6e0
trap_fatal() at trap_fatal+0x391/frame 0xfffffe002eb0b740
trap_pfault() at trap_pfault+0x4f/frame 0xfffffe002eb0b790
trap() at trap+0x286/frame 0xfffffe002eb0b8a0
calltrap() at calltrap+0x8/frame 0xfffffe002eb0b8a0
--- trap 0xc, rip = 0xffffffff811eef8e, rsp = 0xfffffe002eb0b970, rbp = 0xfffffe002eb0b9c0 ---
vmspace_fork() at vmspace_fork+0x95e/frame 0xfffffe002eb0b9c0
fork1() at fork1+0x356/frame 0xfffffe002eb0ba60
sys_fork() at sys_fork+0x54/frame 0xfffffe002eb0bac0
amd64_syscall() at amd64_syscall+0x387/frame 0xfffffe002eb0bbf0
fast_syscall_common() at fast_syscall_common+0xf8/frame 0xfffffe002eb0bbf0
--- syscall (2, FreeBSD ELF64, sys_fork), rip = 0x8003ed8ea, rsp = 0x7fffffffe558, rbp = 0x7fffffffe590 ---
But we see some errors in the message buffer:
<6>pid 75760 (unbound), jid 0, uid 59: exited on signal 11
<6>pid 4613 (awk), jid 0, uid 0: exited on signal 6 (core dumped)
I would guess that is pfBlocker updating except I don't see that running. In which case do you have a large number of custom Unbound values? Host overrides?
Check the crontab for processes running at 8.00. Installing the cron package will show that.
Steve