The bug causes one extremely loud track to play on loop in Skellige, even overriding combat and gwent music. It's so loud it drowns out voices in conversations as well. After traveling to Velen (or any other world zone), music will work normally until a save is loaded, at which point the music will disappear entirely in all regions (including combat and gwent) except Skellige. Travelling back to Skellige will play the extremely loud looped track once again and you're back at square one. There doesn't appear to be any permanent solution to this problem as of yet.

EDIT: Further testing has narrowed the trigger point down to the quest Coronation (a very short quest that immediately follows King's Gambit, which is completed by simply going to a location). Specifically, it appears to trigger when you arrive at the Coronation and get the cutscene where the king/queen is announced, so the bug is perfectly avoidable by simply telling Crach you'll join them at the Coronation later, allowing you to complete King's Gambit and avoid the bug until it's fixed.

I also only tested this on Cerys' path and am unsure if Hjalmar's has the same issue. Also, I'm not COMPLETELY sure whether it's the Coronation cutscene that triggers it or simply entering the area, although I believe it is the former since that is where the first instance of the very loud track that permanently loops in Skellige as a result of the bug can be heard.

Same problem.

I don't know if you saw my reply to you on Reddit, so I'll post it here too.

The only solid solution found so far is completing the quest Isle of Mists, however this is a very late-game quest and most people that have this bug are nowhere near it yet.

There is another solution on that I found, however this one didn't work for me, and that is to play a round of Gwent in Skellige.

The solution that worked for me was to fulfill a witcher contract, and either die or force quit and restart (without saving) the game during the fight with the monster.

I think that this forces the game into giving you the boss music and thusly overrides the glitch.

I went back on the no music save and tested it with the following quests:

The Oxenfurt Drunk - Katakan (Oxenfurt)- success
Strange Beast - Nekker Warrior (Skellige)- success (this is the one I did first)
Nameless - Morkvarg (Skellige)- success
The Merry Widow - Grave Hag (Velen)- success

Can anyone else confirm?

Exactly the same problem, and I'm glad that I didn't finished the Oxenfurt Drunk before. Saved my game, thank you!

Is there any easier way?

The bug is strange - I reinstalled the game, cleared the savegames - still no music.