So I think I've might have found the culprit. It's not bluetooth or one of the virtual audio plug-ins.
It's the USB cable (DJTT) that I used with my DDJ-1000. I feel like an idiot.
I swapped it with another USB cable I was using (also DJTT) after 2 days because it was angled. And I think that is when the issues started arising as I was on the mixer/computer longer. Having swapped it back and also trying the default one that the S11 came shipped with, I'm not experiencing the audio/video issue anymore (so far).
What's odd is that the DDJ-1000 doesn't prompt the audio issue with the same cable the S11 has an issue with.