Hi Robert - great to hear from you again. Thank you for taking the time to provide your response. I believe the problem has now been resolved!
Based on your response, I moved the Orbi from a spare bedroom location to my main equipment closet. Previously, I was only using the Orbi to provide WiFi connectivity to my iPhone, iPad and some security cameras, thermostats, etc. All my audio components were connected via Ethernet from the AT&T router and an unmanaged Netgear switch.
With the Orbi to the equipment closet, the Orbi WAN input comes directly from the AT&T router. The unmanaged switch and the Nucleus are now directly connected to the Orbiās switch ports. Everything is now getting 10.X.X.X IP addresses. Previously, the devices connected to the AT&T router or unmanaged switch received 192.168.X.X IP addresses and the WiFi devices received 10.X.X.X addresses. After rebooting everything, the Roon client now comes up as it once did. My quick ops check seems to indicate everything operating again as it once did.
Iām very happy to have Roon working again! Itās still a head scratcher to me why the previous configuration āworkedā for two months and then didnāt. As Conner suggested, an updated baseline may have had an unintended consequence. In any case, the current configuration is more straightforward and hopefully will serve as a long term fix. Iām going to run with this over the weekend. If no issues resurface, Iāll ācloseā the issue.
Thanks again!!