Wow, more weirdness. I verified the Pi does not specify its own address, it is getting its IP address from DHCP. (The file /etc/dhcpcd.conf has everything commented out, the Pi defaults to using DHP).
I got up today and found the Pi at a new address (...40) and the gateway shows ** static ip address** for it:
which makes no sense at all, as there is nothing in the static lease table for this MAC address or the ...40 IP address:
So what the heck?
A few minutes later I lost my SSH connection with the Pi, and I now find it at a new address (...16) with no **static** notation in the gateway:
Is this Ubee gateway just junk? This makes no sense.
I am tempted to just configure the Pi to take the ...200 address (e.g. actually configure a hard coded static address in the Pi) and forget trying to do this with the DHCP server in the gateway. I don't iike it because this Pi will be moved to other networks where that address might not be valid. Ugh.
OMG I am such an idiot. I have the Pi connected by ethernet cable to the gateway. But the Pi model 3B+ also has an on board wifi module. Both interfaces are enabled by default. I have been trying to get this address assignment working on the wired interface - but the wifi interface was also active (with a different MAC address).
Not sure how they interact in this scenarios, but it seems to mess up the assignment of the wired MAC address.
I disabled the on board wifi module and viola! the fixed DHCP assignment now works as expected on the wired ethernet interface. Turns out the fixed address must, in fact, be INSIDE the DHCP assignment range (which makes some sense as this is in fact an address assigned by DHCP). The word "static" in "static lease" in the gateway UI may be confused with "static IP configuration' in the client device which is completely different. A better term would be "fixed lease".
Thanks for all the help, as usual, "user error" :-)
Glad that you sorted out the issue.
As for the static lease, I use openwrt and all assigned static IPs need to be inside dhcp range of the router - the same that you witnessed.