I have the exact same issue.
I got a replacement mainboard due to this issue (Piece of mainboard partially melted).
My old board works perfectly fine (audio wise) switching between old the and new board one has working audio ther other doesn’t.
@Kieran_Levin Does this suggest hardware issue?
I get all the same output from dmeg as other above do “no response from codec”
Also seeing constant CPU activity of 1-1.5% with the new board and generally higher power drain though I don’t know if that is related.