I am using the USB output to the DAC. It was working fine until I let it do a software update. It gets files from Qobuz, which I can play to the HDMI output. But when the remote says it is playing to the DAC, I get no sound. Feel free to call me.
You posted a screenshot from Roon rather than a screenshot of the Web Administration Interface of your Nucleus as requested - but no matter, it seems as though your Nucleus is working as expected.
Have you tried rebooting your DAC to see if the USB communication between it and the Nucleus can be restored?