Hi @Tormod_Guldvog,
Thank you for your post.
One of the myriad network security changes introduced with MacOS 15.x was MAC address randomization.
I recommend navigating to your Network settings (WiFi → Details) and checking whether the Mac in question is relying on a Fixed, not a rotating, Private WiFi Address.
This will not be a panacea - the team has a ticket for ongoing Sequoia issues which also match your reported symptom. Roon interacts with coreaudio, the Mac audio daemon, via the loopback interface. Sometimes, Sequoia will interrupt RAAT’s access to that interface. Our Developers are investigating the issue diligently and proving updates as available here: Roon on MacOS 15.0+ Sequoia: Audio Zones Disappear, Requiring Local Network Access Reset or RAAT/Roon/macOS Restart [Roon Investigating]
We hope to have a more fruitful update soon. Thank you for your patience.