Thanks for writing in, and welcome to the community! Apologies for the delay in getting to your thread - the first thing to do if you haven’t yet, would be to give both your Roon Server device and your router a hard reboot, leave both unplugged for a few minutes before rebooting.
Let me know if you’re still not seeing the DAC after that. If not, do you have another USB cable you could try, as well as testing another USB port?