I noticed for the first time(maybe it happend and earlier but sometimes when dozens of enemies shoot at me and all blown up across battlefield, I don't give to it much attention,but immersion suffers) when fought in the story mission, a Gaping Wound(First Khorne Story Ark) when it made my way to the warp gate with Gaius Thorne,music was playing 3-4 minutes, until I came and killed similar to the dreadnought unit Khorne(Bloody Executioner Impaler). After I performed with a some more missions of different orientation(in all of them music played),faced with a similar problem: the type of Siege mission,the type of enemies - the Rebel guards,the type of terrain-distant Islands,after 3-4 minutes the music was gone(but when i was fighting with the same mission type and terrain,but enemy was Nurgle all plays normal),another mission, too, the Siege,the enemy - the Rebel guards,the type of terrain-a Ruined City, after the start of the mission 3-4 minutes the music disappears.Played alone for a Crusader armed with a shield and a sword.