Not only a restart of Roon, also the Mac. This has worked for me so far, without fail:
- Stop the Roon app
- Reboot the Mac. I’ve also had success with just toggling on and off again the WiFi connection of my Mac without rebooting!
- Start the Roon app
But I’ve seen other people reporting that this didn’t work for them. Nevertheless, for me it did work for which I’m very glad.