So, I’ve been trying to simplify my setup a bit. I’ve found that usb attached storage to ROCK, rather than my NAS (which happily serves the BS app) seems to increase reliability. Specifically fewer dropouts in BS logs and the end of dropouts to an RPi.
Also, having made my Flex the master clock, I’ve had some prolonged listening with 2 zones in sync. However, as soon as I skip a track, they’re out of sync again. @Eric, not sure if this adds anything new to the picture?
Fwiw, other network changes (eg cabling both Node 2 and Flex directly to ports on the same switch) made no difference.