This may or may not be relevant to the issue.
Sometimes on my mid 2012 MBP, closing a Firefox youtube tab will somehow ‘unlatch’ the Quantum 2626 driver, which will stop passing sound. The Audio Midi Setup window shows it as having 0in/0out at this point.
A hard reset, usually disconnecting/reconnecting the TB cable, or when that doesn’t work, power cycling the Q2626, or when it’s being particularly stubborn, power cycling the Macbook does the trick.
Now using Brave Browser for Youtube / streaming. No issues. (Safari spins the fans up too much so won’t use that.)