From my own experience it’s upsampler, because I have made a test.
When distortion happens, I stop the music and then I reboot DAC, but clock and upsampler stay power on, play same song and distortion remains.
So I tried another way, reboot the upsampler, but clock and DAC stay power on, play same song and then distortion just gone, eveything sounds normal.
I believe there are some people experience same problem too.
Upsampler stuck - Support - dCS Community
Distortion after sample rate change - Support - dCS Community
Muted sound on my Vivaldi - Support - dCS Community