Assigning Static IP Address To Device Not Working?

I am afraid that you are caught in the tangled web of Orbi DHCP assignment.  Once a device has received an IP address from the Orbi, that assignment seems to take precedence over the value recorded in the LAN Setup table.

My practice (just personally) is to enter new devices into the LAN Setup table before connecting them to the network. Most smart plugs have the MAC address printed on the product label, often on the back of the case where the electric plug is.  When I do this step first, then gizmos always get the IP address I want them to have.

When I have neglected to perform this step and a device has an IP address that is not what I want it to have, I use this procedure to force it to change:

• Dig out the old cell phone that I no longer use as my "daily driver". (no SIM card in it) - or use a laptop
• Unplug the offending smart plug
• Go into network settings on the phone/laptop and set the phone/laptop to a Static IP address* that is the IP that the smart plug has gotten by accident
• Connect to the Orbi WiFi
• Verify on Attached devices that the phone/laptop is connected and has taken the IP address
• Then, connect the smart plug.  This time, the plug will say, "give me the IP I had last time", but the Orbi will do an ARP request "does anybody already have this IP?", find that the phone/laptop has it, and give the smart plug the IP that is in the LAN setup table.
• (I have also done this Static IP process with a laptop.)

* This is sort of an OCD thing, but "Static IP" usually refers to an IP address that has been set on the device itself, whereas "reserved IP" or "assigned IP" refer to the process of having the network assign a specific IP to a device.