i have the same problems as you OP. had these problems since beta, sent plenty of tickets about it.
The game can be so nice at times, when i have the ambient sounds, the music, the cinematics/voice over all at once, it gets pretty epic but then i will start having the ambient sounds loop or vanish, same with music...i really wish there was continuous music too ... but the worse, the very worse is when i lose all of it except the sound of my footsteps, no sound at all, just footsteps with a bit of echo to it, it sounds terrible. huge immersion breaker for me but i just hope they can fix it or whatever