I was posting above and figured out my problem. I will share it as it might give you a clue.
It has to do with Wake On LAN not working properly somewhere along the chain. I never had this problem before, so i don’t know why it has started.
My core is a new M1 Mac Mini and Big Sur. Client apps are sometimes iphone, ipad, or Mac laptop (mostly the latter for my testing).
For whatever reason, Wake On LAN is only partially giving access to Roon. You can see the library but not audio devices. I tested by setting my “Turn Display Off” to 1 min on the Roon core mac. On a client (mac laptop), turn off Roon, wait a bit, turn it back on and it connects but does not find audio devices. If i hit the keyboard or mouse on the sleeping mac mini, Roon shows the end points in about 1.5 seconds (pretty fast).
For now, I set this to Never unless someone has a better solution. Searching the forum here on “Wake on LAN audio devices” finds similar cases.