Why does the DAC not lock to the Master Clock (set to 44.1kHz) when I change the Upsampler's output from DSD or 176.4kS/s to 192kS/s?

The DAC can only lock to word clock if the data sample rate is an exact multiple of the clock frequency. 176.4kS/s and DSD (2.8224MS/s) are exact multiples of 44.1kHz (x4 and x64 respectively) so there is no problem. 192kS/s is 44.1kHz multiplied by 4.35374149659864 – this is not an exact multiple, so the DAC cannot synchronise the two rates.