I've seen mention of this in posts with different topics and I'm pretty sure you are aware but I thought to mention this specifically.
If this is a redundant post, please ignore this.
Over the past few weeks, when playing co-op or solo, the sound disappears completely.
Not only from the game but also from the console. The only thing still working is de sound from e.g. the captain speaking through the controller audio during a mission.
Completely quitting the game restores all sounds, including the sound from the console.
After starting up the game again, the sound will be all right, until -at random it seems- the sound disappears again.
This does not happen very often, but often enough to feel it.
I haven't had this problem in a very long while and it seems it's back since a couple of weeks ago.