Roon always tries to start a stream at the native rate first. If your DAC or driver says “no”, then it progressively backs off to easier formats. So if it’s resampling, then the DAC or driver refused to play the audio stream.
One of the most common reasons that this happens is if you had another exclusive mode app consuming the device and tried to play a certain format through Roon. Roon remembers (and bans) failed configurations for the duration of the application run, so that it doesn’t waste too time trying them later–so one failure is enough to cause that format to be resampled until the app is restarted.
If you’re still seeing this reboot after a reboot, and with no other apps vying for your audio device, it might be useful to pull logs and look at exactly how the DAC/driver are saying “no” to Roon.