I have the same problem, with the same combat music (b6e27). I can remove it and everything is OK, but after I exit the game and then load again, that music starts, and it starts during the initial loading screen (the screen that shows a picture and some info or hints). It is VERY annoying! (And this problem also started for me at the same situation, after the fight with the 2 assassins.)
This is just a layman's guess:
I assume that normally when enemies are killed, there is some trigger that turns off the combat music, but maybe since the assassins don't actually die, the trigger to end the combat music isn't triggered.