Thank you for the report. Certain events might trigger the Mac OS firewall to sever the connection between RoonServer and the Roon GUI app on the same machine (a MacOS update, certain Roon updates, etc.). Are you able to confirm whether your Mac OS firewall is active, and whether you have any exceptions in place for RoonServer and RoonAppliance?
If that doesn’t work, then I recommend fully refreshing RoonServer to verify there’s not a cached associated with a defunct database. Verify you have a Backup first for due diligence.