I’ve been debating whether to post this since I have (somewhat) resolved the issue.
I was using a cable internet connection and for convenience sake I had both my modem and my router in the upstairs ‘office’. I have a few switches, including one in the cellar to which I run an Ethernet connection from the upstairs router. All was good.
I switched ISPs to a fiber connection and I didn’t have the installer run the in-house connection upstairs and instead left it in the cellar. I left my router upstairs and, rather than running a line up to the router and another back down to the cellar switch, I connected the output from the fiber device to the switch and then from the switch to the upstairs router.
Surprisingly, that worked. All my addresses stayed as I had assigned them, i.e. 192.168.0.xxx and everything connected successfully. All my smart hubs and devices, my smart TVs, ROKU, and AppleTV were all good. Everything was good, except for ROCK.
ROCK originally had an good intra-network connection of the 192.168.0.xxx type. However after a short time and (presumably) after it called home, the software decided that my ROCK device’s address was the internet address of my router, i.e. 184.12.xxx.xxx. A different sub-net from all my other devices. Obviously, that wouldn’t work.
Problem was solved by moving my router to the cellar and making it the first stop for the fiber connection coming into the house. Just a curiosity, FWIW.