I would reboot your Roon server anytime you start having problems or it starts seeming slower than normal. An occasional reboot of your router can be a good idea also.
Hi @David_Pullum,
Thanks for writing in to ask us about this issue. Do you have multiple subnets on your home network? This screen means that the Roon app isn’t finding your server where it expects it to be on your network so. So it could be a subnet issue. Roon devices cannot communicate with each other if they’re in different subnets. Its also possible the the LAN IP address of your server has been changing without your knowledge. To test that you can set a static IP address for your server.
Please try the troubleshooting steps and let us know how it goes.