I’m having a similar issue with my NUC8i3. When I first set it up about 6 months ago the NUC ran 24x7 without any issues. It was after one of the Roon updates a couple of months ago that it started to misbehave. The NUC server thinks its streaming audio to it’s USB connect DAC, or through the HDMI to my AVR. But, there’s no audio. I have to reboot the NUC to get it to work again. Then it works fine for a day or 2. If I could get it to reboot itself every night, it would be a viable workaround. My NUC has the latest BIOS and I looked for any type of scheduled reboot option in it, but it doesn’t have this feature.
One thing I noticed is that when the Roon server software is failing to stream audio to physically attached devices like the DAC or AVR, it is still able to stream to remote devices. I have a couple of Raspberry Pi’s running Ropieee and they seem to be unaffected and continue to function. I’m not 100% sure yet, but it seems (for me anyway) to just be an issue with directly attached devices. So, as another potential workaround I setup a RPi with Ropiee and have it feeding the same DAC via USB, rather than the NUC itself. It’s only been a few days, but so far so good.