How do you remove a duplicate "down" host?

I think you can remove the offending host by using qbadmin and referring to it by the MAC address:

qbadmin worker --remove 00:30:48:5A:71:5D

If that doesn't worker, you'll need to remove it by name or IP:

qbadmin worker --remove LAX-RF-029

If you're lucky, you'll get the down host removed. If both get removed, just use --clearbanned and restart the Worker:

qbadmin worker --clearbanned