I am losing my mind over this. This should be such a simple thing but ER605 is refusing to release IP address assigned to specific MAC address after deleting it or changing it.

I have many static IP addresses reserved. There is one piece of hardware where I assigned a static IP address under "Network -> LAN -> Address Reservation". I now stopped using that piece of hardware and have replaced it with a new piece of hardware. I want to use the EXACT same static IP address for that new piece of hardware as the old one, since this new piece of hardware is a replacement/upgrade for the old one.

I have tried so many things but ER605 absolutely refuses to release the static IP that was assigned to the MAC address of the old unit. I have not yet rebooted ER605, I expect this to work without rebooting. The old MAC address-static IP address binding is still showing up under DHCP Client List. I did several things, none of which work:
- Changed MAC address from old to new; does not work, new device gets new DHCP address and not the static one

- Deleted address reservation then created new one with new MAC address; same thing

- Changed lease time to 1 minute, shut down new unit, waited longer than 1 minute, started again, same thing

Why is this happening? Why is ER605 refusing to let go of that address reservation? This if frustrating.