During some testing I tried moving an interface with an IP configured on it into a vnet kernel, which paniced (I assume, since the machine rebooted) the kernel
(In reply to Gijs Peskens from comment #0)
Sigh I was tired when I typed this "vnet kernel" -> vnet jail.
create jail with vnet enabled, without interfaces
ifconfig epair create
ifconfig epair0b inet 18.104.22.168/24
ifconfig epair0b vnet yourjail
I'm unable to reproduce this. Do you have a crashdump, or at least a kernel panic message?