Looking at the ChatGPT log, it looks like it's very politely telling you that one of your switches is not a switch, but a router!
As I said, a blindingly obvious misconfiguration.
Yes. Problem was it’s no longer on the network. I had experimented with using an old router as a switch, trying to turn off the WiFi and router functionality. It didn’t work, so I removed it. However Windows remembered it was there and then couldn’t decide which router to use for DHCP. Crock of ****!