Sounds like a drive error. Linux never quits, especially if left alone.
That CPU is unlikely to give you a good Roon experience. It runs a pretty big database which should ideally sit on SSD and there's a lot of data points to process in the UI, plus volume levelling, and other DSP (e.g. downsampling stuff your DAC can't natively play, volume leveling, upsampling, convolution and parametric EQ if you choose to) so I'd really recommend a much higher spec NUC. They're a few weeks away from releasing their own distribution called Roon Optimized Core Kit (ROCK) which would be a turnkey Roon solution. I'd move in that direction if you want to keep a NUC type footprint.