Thanks for the reply.
Yes I can play through my Samsung phone as an endpoint…with the D400 switched off.
Network is a BT hub with the Core plugged into the ethernet port on an extender in a mains socket (nothing else in that socket) in tbe room with my hifi. There are no issues finding the Core over wifi from the phone which I use as the Roon control, or from my macbook which also has the Roon app installed. .
The issue seems to be specifically with the interaction with the.Core and Devialet D400. They are connected via USB. It worked fine until this most recent build update.
I have disabled tbe wifi on the D400 in case that was causing conflicts but it made no difference.