Still having a very specific issue after MacOS Sequoia upgrade. The iMac is a Roon endpoint. SGC Sonic Transport i7 is the ethernet-connected Roon server. After the iMac received the MacOS Sequoia update it either does not see itself as an endpoint that can be enabled, or if it does, it acts as I initially reported, that is Roon reports “too many failures, stopping playback” when using the equipment connected as an endpoint (Astell & Kern AcroL1000).
Updated MacOS 9/23. Roon will not play tracks initiated from updated iMac but will from an iPad - “too many failures, stopping playback”
After upgrading to Sequoia, if playback has problems, go to system settings-> privacy&security-> local network. Toggle the Roon entry off and on. It fixed my problem.