I lifted pin 8 using a small needle and that did indeed fix my issue. Temperatures on U6 and U8 are normal now and OSSC seem stable. No audio anymore thru the OSSC of course.
As to what could have caused the damage in the first place. I mentioned I recently got a new Amiga 1200 and this issue happened sort of the same time as I got it, although not sure.
Is it possible for the sound output from my Amiga could have destroyed the ADC in my OSSC? Or is it more likely this was coincidental and I just had bad luck with a failing chip?