Hi,
The error appears to be on the RS520 side of things.
My mac was connected via ethernet (even though wi-fi is on. ) [Note: Ethernet connection takes priority]
The Mac’s settings are for full performance and power when connected to a power supply. Not sure what is ‘clam shell mode’ although I do run it w a docking station , two monitors and an external keyboar / mouse.
While I couldn’t see the RS520, I could see other airplay enabled devices.
The RS520 had an ethernet connection so its wi-fi was off.
I checked the streaming settings… while normally all are turned on… they were all turned off.
Not sure how they were turned off.
Its not the router and the wi-fi router has both the 2.4GHz and 5GHz bands and the Apple mac is always on the 5GHz.
Will continue to monitor the situation.