The Bluesound and usb output have been problematic with Roon for some time this isn’t your DAC or network. There have been many post covering the same problem.
You won’t see the DAC in Roon via the Node as all outputs are active at once so Roon assumes you’re using the internal DAC which is how it’s tested for the main part and not via the external DAC options as it doesn’t feedback to tell Roon which output is being used. This is how BluOS have implemented it. Not sure if Roon Ready is even tested via the USB output at all especially on the older nodes it was added via a firmware update and Roon doesn’t redo the certification process again for firmware updates.