A bhyve guest is unable to connect to the network after it’s host was configured to use NIC aggregation.
The guest’s vm switch was configured to use one of the NIC aggregation’s ports instead of the interface itself.
This was evident by:
[root@T20][~]# vm switch list NAME TYPE IDENT VLAN NAT PORTS public auto bridge0 - - em0
In the above listing, public should be using lagg0.
Remove the em0 port from public and add lagg0 to it:
vm switch remove public em0 vm switch add public lagg0
At this step I choose to simply restart the guest after which it was back on the network.