I’m not sure exactly what triggers it, but when running the Cerim Crucible there will be times when the audio bugs out, causing certain sounds to not play. Most of these sounds relate to abilities and attacks being used by both the player and the enemy. I can’t fix it unless I exit the game completely and relaunch, which kicks me out of the crucible.
This becomes really annoying when fighting the boss, since there are times when it’s completely off screen and I can’t hear what it’s doing.