Basically what the title says. This bug started at some point in Skellige and I've found no way to fix it.
I've seen a few Reddit posts about it but haven't seen anything posted on this forum.

Important to note my game is Mod Free. I also played the game back in 2015 when it was first released and never had game breaking bugs so being on version 4.03 feels like a downgrade in some ways.

Here's what I tried:
_ Uninstalled / Reinstalled the game
_ Verified / Repair game files
_ Sent a message to CD projekt but reply was unhelpful
_ In game tried the killer whale potion but it didn't do anything
_ Travelled to all available maps to see if the problem persisted in all locations and it did

The only short term solution for now is to use white raffards and swallow when going underwater but that still means I can only be underwater for 10s at a time.

This problem also means that the skellige quest "King's Gambit" is impossible to finish as once you're in the cellar with the toxic fumes there is nothing that can be done to recover your breath and so you die no matter what.

Just sharing to see if anyone else has been getting the same problem, but if it's the same as people on reddit then I guess I can only hope for a patch soon.