This is weird. I took the deck A rca cable out of the mixer to feed direct into the UCA202 to monitor through the headphones, but the sound magically was still coming out of the mixer(!) - and i can still fully control the deck A. It seems as though the decks are swapping use of each others soundcard, but the control of each deck remain as you would expect.

Update a quick reboot and reconnect later and each deck is assigned to the right output A to 1 and B to 2. I did try the sound direct out of the CDJ and bypassed the mixer and the distortion still exist ive tried several other track and the
sound derogation/distortion is still their some worse than others
only though Output 2.
Happy to assist the mixvibes crew explore what going on to sort this.