You’re already signed in message. This happens quite a lot. I know there is a work around (unauthorize), but I consider this as a bug which needs to be addressed.
One possibility - you are actually signed in on a second RoonServer instance somewhere on this network.
Looking through post history and diagnostics, you migrated your RoonServer between two machines at some point. Did you fully remove the RoonServer database from the previous machine? Do you frequently migrate RoonServer between machines?
If your screenshot is from the Mac Mini itself and not a second machine: have you restored from a Time Machine backup, cloned any drives, or otherwise copied RoonServer at any point?
Have you changed root permissions, or installed RoonServer in a location inaccessible to the current user?
Thanks for confirming the above. We’ve activated diagnostics for your account and according to the screenshot timestamp, it looks like Roon was having more issues than just authorizing the server, it was also failing to get the current time from the time servers, connecting to Qobuz services and getting the local radio stations list. Do you usually open Roon right as the computer starts up? I wonder if there could possibly not be enough time after startup for the Mac to properly establish a network connection?
Roon server auto loads at start up. Roon client runs on an iPad which I use several seconds after the server started. During startup, besides loading Roon, other processes launch which take a long time (1 min), giving Roon plenty of time to initialise.
??? Roonserver isn’t a normal app. It doesn’t even appear in the apps folder. It’s a service which always auto loads (I think). Or does it start by starting the Roon client app?
No, @daniel is referring to the Roon Server app, which runs in the background in Windows or MacOS. When running, it should be present in the section of the Windows Taskbar used to display running background applications. Similarly for MacOS.
Rightclick on the Roon Server icon here to display its menu. See:
The option to have Roon Server open on startup can be accessed by right-clicking the Roon Server icon in the bottom right (in the taskbar area reserved for background applications).