As title says, the map has not bgm whatsoever. It plays character selection bgm, housing bgm and after leaving the dungeon is just silence
Have this same problem but with wildhuter characters while playing Bai.
Playing with wolf dogs (Levia at least) it uses CM_TOWN_BGM10_1 but I am not sure if that is the correct bgm for Busan tho..
With Black Lambs I am not sure since I have not done Busan on them.
Seems to only play music after you finish the story there.